10.02 ACHNATHERUM P. Beauv.

Mary E. Barkworth

Plants perennial; tightly to loosely cespitose, sometimes shortly rhizomatous. Culms 10–250 cm, erect, not branching at the upper nodes; basal branching extra- or intravaginal; prophylls shorter than the sheaths. Leaves sometimes concentrated at the base; sheaths open, margins often ciliate distally; cleistogenes not present in the basal leaf sheaths; collars sometimes with hairs on the sides; auricles absent; ligules hyaline to membranous, glabrous or pubescent, sometimes ciliate; blades flat, convolute, or involute, apices acute, flexible, basal blades not overwintering, flag leaf blades more than 10 mm long. Inflorescences terminal panicles, usually contracted, sometimes 2 forming at the terminal node; branches usually straight, sometimes flexuous. Spikelets usually appressed to the branches, with 1 floret; rachillas not prolonged beyond the floret; disarticulation above the glumes, beneath the floret. Glumes exceeding the floret, usually lanceolate, 1–7-veined, acute to acuminate, sometimes obtuse; florets usually terete, fusiform or globose, sometimes somewhat laterally compressed; calluses 0.1–4 mm, blunt to sharp, usually strigose; lemmas stiffly membranous to coriaceous, smooth, usually hairy, sometimes glabrous, hairs on the lemma body to 6 mm, usually evenly distributed, hairs on the upper 1/4 sometimes somewhat longer than those below, not both markedly longer and more divergent, apical hairs to 7 mm, lemma margins usually not or only weakly overlapping, firmly overlapping in some species with glabrous lemmas, usually terminating in 0.05–3 mm lobes, sometimes unlobed, lobes usually membranous and flexible, sometimes thick, apices with a single, terminal, centric awn, awn-lemma junction evident; awns 3–80 mm, centric, readily deciduous to persistent, usually scabrous to scabridulous, sometimes hairy in whole or in part, if shorter than 12 mm, usually deciduous, not or once-geniculate and scarcely twisted, if longer than 12 mm, usually persistent, once- or twice-geniculate and twisted below, terminal segment usually straight, sometimes flexuous; paleas from 1/3 as long as to slightly longer than the lemmas, usually pubescent, 2-veined, not keeled over the veins, flat between the veins, veins usually terminating below the apices, sometimes prolonged 1–3 mm, apices usually rounded; lodicules 2 or 3, membranous, not lobed; anthers 3, 1.5–6 mm, sometimes penicillate; ovaries with 2 style branches, branches fused at the base. Caryopses fusiform, not ribbed, style bases persistent; hila linear, almost as long as the caryopses; embryos 1/5–1/3 the length of the caryopses. x = 10 or 11. Name from the Greek achne, ‘scale’, and ather, ‘awn’, a reference to the awned lemma.

As interpreted here, Achnatherum is one of the larger and more widely distributed genera in the Stipeae. It is difficult to estimate how many species it contains because its boundaries are still unclear. Of the 28 species in the Flora region, only A. splendens, from Europe, is introduced.

Most species of Achnatherum used to be included in Stipa, a genus that at one time included almost all Stipeae with an elongated floret. Keng (cited in Tsvelev 1977) transferred some Chinese species of Stipa sensu lato with blunt calluses and less indurate lemmas than Stipa sensu stricto to Achnatherum, a realignment that Tsvelev (1977) supported. Thomasson (1978) demonstrated that several North and South American species of Stipa had lemma epidermes similar to those of the Eurasian species of Stipa that had been transferred to Achnatherum. After considering various additional characters (Barkworth 1981, 1982), Barkworth (1993) transferred most North American species of Stipa and some of Oryzopsis into the expanded Achnatherum. In retrospect, her transfer of South American species to Achnatherum was ill-advised. Some have since been transferred to Amelichloa (Arriaga and Barkworth 2006), others to Jarava (Peñailillo 2002). With its current boundaries, Achnatherum is probably still polyphyletic (Jacobs et al. 2006), but the evidence does not support return of the North American species treated as Achnatherum to either Stipa or Oryzopsis.

In the key, glume widths are the distance between the midvein and the margin. Floret lengths include the callus, but not the apical lobes. Floret thickness refers to the thickest part of the floret.

 

SELECTED REFERENCES Arriaga, M.O. and M.E. Barkworth. 2006. Amelichloa: A new genus in the Stipeae (Poaceae). Sida 22:145–149; Barkworth, M.E. 1981. Foliar epidermes and the taxonomy of North American Stipeae (Gramineae). Syst. Bot. 6:136–152; Barkworth, M.E. 1982. Embryological characters and the taxonomy of the Stipeae (Gramineae). Taxon 31:233–243; Barkworth, M.E. 1993. North American Stipeae: Taxonomic changes and other comments. Phytologia 74:1–25; Barkworth, M.E. and J. Linman. 1984. Stipa lemmonii (Vasey) Scribner (Poaceae): A taxonomic and distributional study. Madroño 31:48–56; Cheeke, P.R. and L.R. Shull. 1985. Natural Toxicants in Feeds and Poisonous Plants. AVI Publishing Company, Westport, Connecticut, U.S.A. 492 pp.; Epstein, W., K. Gerber, and R. Karler. 1964. The hypnotic constituent of Stipa vaseyi, sleepy grass. Experientia (Basel) 20:390; Freitag, H. 1985. The genus Stipa in southwest and south Asia. Notes Roy. Bot. Gard. Edinburgh 42:355–487; Hitchcock, A.S. 1951. Manual of the Grasses of the United States, ed. 2, rev. A. Chase. U.S.D.A. Miscellaneous Publication No. 200. U.S. Government Printing Office, Washington, D.C., U.S.A. 1051 pp.; Jacobs, S.W.L., R. Bayer, J. Everett, M.O. Arriaga, M.E. Barkworth, A. Sabin-Badereau, M.A. Torres, F. Vázquez, and N. Bagnall. 2006. Systematics of the tribe Stipeae using molecular data. Aliso 23:349–361; Johnson, B.L. 1945. Natural hybrids between Oryzopsis hymenoides and several species of Stipa. Amer. J. Bot. 32:599–608; Johnson, B.L. 1960. Natural hybrids between Oryzopsis and Stipa: I. Oryzopsis hymenoides × Stipa speciosa. Amer. J. Bot. 47:736–742; Johnson, B.L. 1962. Amphiploidy and introgression in Stipa. Amer. J. Bot. 49:253–262; Johnson, B.L. 1962. Natural hybrids between Oryzopsis and Stipa: II. Oryzopsis hymenoides × Stipa nevadensis. Amer. J. Bot. 49:540–546; Johnson, B.L. 1963. Natural hybrids between Oryzopsis and Stipa: III. Oryzopsis hymenoides × Stipa pinetorum. Amer. J. Bot. 50:228–234; Johnson, B.L. 1972. Polyploidy as a factor in the evolution and distribution of grasses. Pp. 18–35 in V.B. Youngner and C.M. McKell (eds.). The Biology and Utilization of Grasses. Academic Press, New York, New York, U.S.A. 426 pp.; Johnson, B.L. and G.A. Rogler. 1943. A cytotaxonomic study of an intergeneric hybrid between Oryzopsis hymenoides and Stipa viridula. Amer. J. Bot. 30:49–56; Matthei, O. 1965. Estudio crítico de las gramíneas del género Stipa en Chile. Gayana, Bot. 13:1–137; Maze, J. 1962. A revision of the Stipas of the Pacific Northwest with special references to S. occidentalis Thurb. ex Wats. Master’s thesis, University of Washington, Seattle, Washington, U.S.A. 95 pp.; Maze, J. 1965. Notes and key to some California species of Stipa. Leafl. W. Bot. 10:157–180; Maze, J. 1981. A preliminary study on the root of Oryzopsis hendersonii (Gramineae). Syesis 14:151–153; Peñailillo, P. 2002. El género Jarava Ruiz et Pavón (Stipeae–Poaceae): Delimitación y nuevas combinaciones. Gayana, Bot. 59:30; Pohl, R.W. 1954. The allopolyploid Stipa latiglumis. Madroño 12:145–150; Scagel, R.K. and J. Maze. 1984. A morphological analysis of local variation in Stipa nelsonii and S. richardsonii (Gramineae). Canad. J. Bot. 62:763–770; Shechter, Y. 1969. Electrophoretic investigation of the hybrid origin of Oryzopsis contracta. Pp. 19–25 in L. Chandra (ed.). Advancing Frontiers of Plant Sciences, vol. 23. Impex India, New Delhi, India. 201 pp.; Shechter, Y. and B.L. Johnson. 1968. The probable origin of Oryzopsis contracta. Amer. J. Bot. 55:611–618; Thomasson, J.R. 1978. Epidermal patterns of the lemma in some fossil and living grasses and their phylogenetic significance. Science 199:975–977; Torres, M.A. 1993. Revisión del Género Stipa (Poaceae) en la Provincia de Buenos Aires. Monografia 12. Comisión de Investigaciones Científicas, Provincia de Buenos Aires, La Plata, Argentina. 62 pp.; Tsvelev, N.N. 1976. Zlaki SSSR. Nauka, Leningrad [St. Petersburg], Russia. 788 pp.; Tsvelev, N.N. 1977. [On the origin and evolution of the feathergrasses (Stipa L.)]. Pp. 139–150 in Problemii Ekologii, Geobotaniki, and Botaniicheskoi Geografii i Floristickii. Nauka, Leningrad [St. Petersburg], Russia. 225 pp. [In Russian; translation of article by K. Gonzales, available from the Intermountain Herbarium, Utah State University, Logan, Utah 84322-5305, U.S.A.].

 

For an interactive dichotomous key, click here; for an interactive, multientry key, click here.

 

1. Awns persistent, basal segments pilose, at least some hairs 0.5–8 mm long ... 2
1. Awns deciduous or persistent, basal segments scabrous or with hairs shorter than 0.5 mm ... 8
2. Flag leaves with ligules 3–8 mm long; lemmas with 1 apical lobe, the lobe to 0.1 mm long, thick, coriaceous ... A. thurberianum
2. Flag leaves with ligules 0.3–3 mm long; lemmas usually with 2 apical lobes, sometimes not lobed, lobes to 1 mm long, thin, membranous ... 3
3. Basal awn segments with hairs of mixed lengths, the longer hairs scattered among the shorter hairs; apical lemma hairs longer than most basal awn hairs ... 4
3. Basal awn segments with hairs that gradually and regularly decrease in length distally; apical lemma hairs usually similar in length to the longest basal awn hairs, sometimes longer on the adaxial side ... 6
4. Florets 8–9 mm long; glumes 1.3–1.9 mm wide from midvein to margin ... A. latiglume (in part)
4. Florets 5–7.5 mm long; glumes 0.6–1 mm wide from midvein to margin ... 5
5. Calluses 0.5–0.7 mm long; paleas 1/2–3/4 as long as the lemmas; palea apices with hairs usually about 1 mm long ... A. nevadense
5. Calluses 0.8–1.2 mm long; paleas 2/5–3/5 as long as the lemmas; palea apices with hairs usually less than 1 mm long ... A. occidentale (in part)
6. Basal blades curling with age, forming circular arcs; paleas 1/4–1/3 as long as the lemmas; panicles 7–11 cm long ... A. curvifolium
6. Basal blades straight to lax, not forming circular arcs; paleas 2/5–4/5 as long as the lemmas; panicles 5–30 cm long ... 7
7. Florets 5.5–7.5 mm long; paleas 2/5–3/5 as long as the lemmas; glumes less than 1 mm wide from midvein to margin ... A. occidentale (in part)
7. Florets 8–9 mm long; paleas 3/5–4/5 as long as the lemmas; glumes 1.3–1.9 mm wide from midvein to margin ... A. latiglume (in part)
8. Lemmas evenly hairy, hairs 1.2–6 mm long, hairs on the lemma body usually not evidently shorter than those at the apices ... 9
8. Lemmas glabrous or with hairs 0.2–1.5(2) mm long at midlength, glabrous or with hairs distally, the hairs at midlength often evidently shorter than those at the lemma apices ... 18
9. Awns persistent ... 10
9. Awns rapidly deciduous ... 13
10. Plants sterile, the anthers indehiscent, with few pollen grains (see discussion following A. hymenoides) ... hybrids of Achnatherum hymenoides (in part)
10. Plants fertile, the anthers dehiscent, with many pollen grains ... 11
11. Sheaths not becoming flat and ribbonlike with age; blades usually involute and 0.2–0.4 mm in diameter, 0.5–1 mm wide when flat; awns twice-geniculate ... A. pinetorum
11. Sheaths becoming flat and ribbonlike with age; blades 0.5–1.5 mm in diameter when convolute, to 7 mm wide when flat; awns once- or twice-geniculate ... 12
12. Awns twice-geniculate, culms 3–6 mm thick ... A. coronatum (in part)
12. Awns once-geniculate, culms 0.8–2 mm thick ... A. parishii (in part)
13. Florets at least 4.5 mm long, fusiform, anthers sometimes indehiscent ... 14
13. Florets 2.5–4.5 mm long, usually ovoid to obovoid, sometimes fusiform, anthers dehiscent ... 16
14. Anthers dehiscent, the pollen grains well formed ... A. webberi
14. Anthers indehiscent, the pollen grains poorly formed ... 15
15. Anthers dimorphic, 1 longer than the other 2; lemmas with 7 veins ... see xAchnella
15. Anthers all alike; lemmas with 5 veins (see discussion of hybrids here) ... hybrids of Achnatherum hymenoides (in part)
16. Panicle branches terminating in a pair of spikelets on conspicuously divaricate, unequal to subequal pedicels, most shorter pedicels at least 1/2 as long as the longer pedicels ... A. hymenoides
16. Panicle branches terminating in a pair of spikelets on loosely appressed, unequal pedicels, most shorter pedicels less than 1/2 as long as the longer pedicels ... 17
17. Panicles 0.5–2.8 cm wide, branches 0.5–5 cm long, strongly ascending; spikelets evenly distributed over the branches ... A. arnowiae
17. Panicles 7–15 cm wide, branches 5–8 cm long, ascending to strongly divergent; spikelets confined to the distal 1/2 of the branches ... A. contractum
18. Apical lemma hairs 2–7 mm long, usually 1+ mm longer than those at midlength ... 19
18. Apical lemma hairs absent or to 2.2 mm long, usually less than 1 mm longer than those at midlength ... 21
19. Calluses sharp; paleas 1/3–1/2 as long as the lemmas ... A. scribneri
19. Calluses blunt to acute; paleas 1/2–9/10 as long as the lemmas ... 20
20. Awns twice-geniculate; culms 3–6 mm thick ... A. coronatum (in part)
20. Awns once-geniculate; culms 0.8–2 mm thick ... A. parishii (in part)
21. Awns 5–12 mm long, readily deciduous, not or only once-geniculate ... 22
21. Awns 10–80 mm long, persistent, once- or twice-geniculate ... 25
22. Lemmas glabrous ... 23
22. Lemmas pubescent ... 24
23. Panicles lax, the branches flexuous, diverging ... A. wallowaense
23. Panicles erect, the branches straight, ascending to appressed ... A. hendersonii
24. Culms 30–250 cm long; plants cultivated ornamentals ... A. splendens
24. Culms 15–25 cm long; plants native in the Flora region ... A. swallenii
25. Terminal awn segment flexuous ... 26
25. Terminal awn segment straight or slightly arcuate ... 27
26. Panicles contracted, all branches straight, appressed or strongly ascending; ligules on the flag leaves to 1.5 mm long ... A. aridum
26. Panicles open, the lower branches flexuous, ascending to widely divergent; ligules on the flag leaves to 4.5 mm long ... A. eminens
27. Panicle branches flexuous, ascending to strongly divergent; spikelets pendulous ... A. richardsonii
27. Panicle branches straight, usually appressed to ascending, sometimes divergent; spikelets appressed to the branches ... 28
28. Flag leaves with a densely pubescent collar, the hairs 0.5–2 mm long; paleas 2/3–3/4 as long as the lemmas ... A. robustum
28. Flag leaves glabrous or sparsely pubescent on the collar, the hairs shorter than 0.5 mm; paleas from 1/3 as long as to longer than the lemmas ... 29
29. Lemma apices 2-lobed, lobes 1–3 mm long; palea veins extending beyond the palea body, reaching to the tips of the lemma lobes ... A. stillmanii
29. Lemma apices unlobed or with lobes to 1.2 mm long; palea veins terminating before or at the palea apices ... 30
30. Apical lemma lobes thick, stiff, about 0.1 mm long; florets somewhat laterally compressed ... A. lemmonii
30. Apical lemma lobes membranous, 0.1–1.2 mm long; florets terete ... 31
31. Lower cauline internodes densely pubescent for 3–9 mm below the nodes, more shortly and less densely pubescent elsewhere ... A. diegoense
31. Lower cauline internodes glabrous or slightly pubescent to 5 mm below the nodes, usually glabrous elsewhere ... 32
32. Glumes subequal, the lower glumes exceeding the upper glumes by less than 1 mm ... 33
32. Glumes unequal, the lower glumes exceeding the upper glumes by 1–4 mm ... 34
33. Paleas 3/5–9/10 as long as the lemmas, the apical hairs exceeding the apices; blades 0.5–2 mm wide; awns 12–25 mm long ... A. lettermanii
33. Paleas 1/3–2/3 as long as the lemmas, the apical hairs usually not exceeding the apices; blades (0.5)1.2–5 mm wide; awns 19–45 mm long ... A. nelsonii
34. Apical lemma hairs erect; lemma lobes 0.5–1.2 mm long ... A. lobatum
34. Apical lemma hairs divergent to ascending; lemma lobes 0.2–0.5 mm long ... A. perplexum

 

1. Achnatherum splendens (Trin.) Nevski
Jiji Grass

Plants cespitose, not rhizomatous. Culms 30–250 cm tall, 2–3 mm thick, glabrous, smooth; nodes 1–3. Basal sheaths glabrous or the margins ciliate, becoming fibrous with age; collars glabrous, including the sides; basal ligules 1–3 mm, membranous, glabrous, truncate to acute; upper ligules to 12 mm, acute; blades to 60 cm long, 2–5 mm wide, abaxial surfaces smooth, adaxial surfaces scabrous. Panicles 12–50 cm long, 4–15 cm wide; branches ascending, usually whorled, longest branches 2.5–15 cm, with 15+ spikelets. Glumes 4–8.5 mm, acute; lower glumes 0–1.7 mm shorter than the upper glumes; upper glumes 0.5–0.9 mm wide; florets 4–7.2 mm, fusiform; calluses 0.3–0.5 mm, blunt; lemmas evenly hairy, hairs at midlength to 1 mm, apical hairs to 1.5 mm, apical lobes 0.5–1 mm; awns 5–12 mm, readily deciduous, indistinctly once-geniculate or flexuous, scabrous; paleas slightly shorter than the lemmas, pubescent; anthers 3–4.5 mm, dehiscent, penicillate, yellow. Caryopses 2–4 mm, fusiform. 2n = 42, 48.

Achnatherum splendens is native from the Caspian Sea to eastern Siberia and south through central Asia to the inner ranges of the Himalayas. According to Freitag (1985), it is a common and typical plant of cold, semidesert regions, growing in groundwater-influenced habitats at elevations of 2100–3800 m. It is rarely eaten by grazing animals, so that it increases in abundance in overgrazed meadows. It is being considered as a potential soil binder for areas in Asia that are too cold for Chrysopogon zizanioides (L.) Roberty.

A.S. Hitchcock (1951) reported A. splendens to be “sparingly cultivated” in the United States. In view of Freitag’s comments, its cultivation in North America should be discouraged.

 

2. Achnatherum stillmanii (Bol.) Barkworth
Stillman’s Needlegrass

Plants shortly rhizomatous, forming open clumps. Culms 60–150 cm tall, 2–5 mm thick, often geniculate at the lowest node, mostly glabrous; nodes 2–3, often puberulent. Basal sheaths mostly glabrous, some-times ciliate distally, intact at maturity; collars glabrous or pubescent, often with hairs at the sides, hairs shorter than 0.5 mm; basal ligules 0.2–0.5 mm, membranous, truncate, ciliate, cilia 0.2–0.3 mm; upper ligules shorter than the basal ligules; blades 3–7 mm wide, lax. Panicles 10–24 cm long, 1.5–3 cm wide, contracted; branches straight, appressed to strongly ascending, lower branches 2.5–3.5 cm. Spikelets appressed to the branches. Glumes subequal, 14–16 mm; lower glumes 1–3-veined; upper glumes 0.6–1.5 mm wide, 3–5-veined; florets 8–10 mm, fusiform; calluses 0.5–1.2 mm, rounded; lemmas evenly hairy, hairs about 0.5 mm, apical hairs similar in length, apices 2-lobed, lobes 1–3 mm, narrow; awns 18–25 mm, persistent, scabrous, once- or twice-geniculate, terminal segment straight; paleas as long as or slightly longer than the lemmas, hairy, hairs about 0.5 mm, veins prolonged, reaching almost to the tips of the lemma lobes; anthers 4–6 mm, penicillate, dehiscent. Caryopses fusiform. 2n = unknown.

Achnatherum stillmanii grows at scattered locations in coniferous forests in northern California, at 900–1500 m, possibly being edaphically restricted. Its combination of large size, long, narrow lemma lobes, and paleal morphology distinguish A. stillmanii from all other North American species of Achnatherum.

 

3. Achnatherum lettermanii (Vasey) Barkworth
Letterman’s Needlegrass

Plants tightly cespitose, not rhizomatous. Culms 15–90 cm tall, 0.5–0.8 mm thick, usually glabrous, sometimes puberulent to 5 mm below the lower nodes; nodes 2–3. Basal sheaths smooth, glabrous, margins not ciliate; collars, including the sides, glabrous or sparsely pubescent, collars of the flag leaves glabrous; ligules 0.2–1.5(2) mm, without tufts of hair on the sides, truncate to rounded; blades 0.5–2 mm wide, abaxial surfaces smooth to scabridulous, adaxial surfaces scabrous or puberulent. Panicles 7–19 cm long, 0.5–1 cm wide; branches straight, appressed to strongly ascending, longest branches 1.2–2.5 cm. Spikelets appressed to the branches. Glumes 6.5–9 mm, subequal; lower glumes 1(3)-veined; upper glumes to 0.5 mm shorter than the lower glumes, 0.6–1 mm wide, 1-veined; florets 4.5–6 mm long, 0.8–1 mm thick, fusiform, terete, widest below midlength; calluses 0.4–1 mm, blunt; lemmas evenly hairy, hairs at midlength about 0.5 mm, apical hairs 0.7–1.5(2) mm, apical lobes 0.3–0.8 mm, membranous, flexible; awns 12–25 mm, persistent, twice-geniculate, scabrous, terminal segment straight; paleas 3–4 mm, 3/4–4/5(9/10) as long as the lemmas, veins terminating at or before the apices, apices round, flat, apical hairs 0.5–1 mm, extending beyond the palea body; anthers 1.5–2 mm, dehiscent, not penicillate. Caryopses about 4 mm, fusiform. 2n = 32.

Achnatherum lettermanii grows in meadows and on dry slopes, from sagebrush to subalpine habitats, at 1700–3400 m. Its range extends from Oregon and Montana to southern California, Arizona, and New Mexico; it is not known from Mexico. When sympatric with A. nelsonii, A. lettermanii tends to grow in shallower or more disturbed soils. It can be distinguished from that species by its generally finer leaves and more tightly cespitose growth habit, as well as its blunter calluses and longer paleas. Its relatively long paleas also distinguish A. lettermanii from A. perplexum.

 

4. Achnatherum nevadense (B.L. Johnson) Barkworth
Nevada Needlegrass

Plants cespitose, not rhizom-atous. Culms 20–85 cm tall, 0.8–1.2 mm thick, usually retrorsely pubescent below the lower nodes, sometimes glab-rous, sometimes pubescent over the whole of the internodes; nodes 3–4. Basal sheaths glab-rous or pubescent, sometimes scabridulous, usually glabrous at the throat, becoming brown to gray-brown; collars, including the sides, glabrous; basal ligules 0.2–0.7 mm, truncate; upper ligules 0.3–1 mm, often wider than the blades; blades usually 10–25 cm long, 1–3 mm wide, usually involute, abaxial surfaces glabrous, adaxial surfaces more or less puberulent. Panicles 6–25 cm long, 0.4–1.5 cm wide; branches appressed, lower branches 2–7.5 cm. Spikelets appressed to the branches. Glumes subequal, 7–14 mm; lower glumes 0.6–0.9 mm wide; florets 5–6.5 mm long, 0.6–1 mm thick, fusiform, terete; calluses 0.5–0.7 mm, sharp, dorsal boundary of the glabrous tip with the callus hairs rounded to acute; lemmas evenly hairy, hairs 0.5–1 mm at midlength, apical hairs 0.8–2 mm, longer than those at midlength and those at the base of the awn, apical lobes membranous, about 0.2 mm; awns 20–35 mm, persistent, twice-geniculate, first 2 segments pilose, with hairs 0.5–1.5 mm and of mixed lengths, terminal segment scabridulous to smooth; paleas 2.8–4.2 mm, 1/2–3/4 as long as the lemmas, pubescent, distal hairs usually about 1 mm, extending well beyond the apices, apices rounded; anthers about 2.5 mm, dehiscent, not penicillate. Caryopses 3–5.5 mm, fusiform. 2n = 68.

Achnatherum nevadense grows in sagebrush and open woodlands, from Washington to south-central Wyoming and south to California and Utah. Johnson (1962) argued that it is an alloploid derivative of A. occidentale and A. lettermanii.

The apical lemma hairs of Achnatherum nevadense appear longer than the lowermost awn hairs. This difference is not reflected in the lengths shown because a few of the basal awn hairs may be as long as those at the top of the lemma, but the majority are shorter. This is the best character for distinguishing A. nevadense and A. occidentale subsp. californicum from A. occidentale subsp. pubescens. In addition, in A. nevadense and A. occidentale subsp. californicum, the hairs on the first awn segments tend to look untidy because of their varied lengths and the different angles they make with the awn; those of A. occidentale subsp. occidentale and subsp. pubescens have basal awn segments with tidier looking hairs.

Differentiating between Achnatherum nevadense and A. occidentale subsp. californicum can be difficult, but they differ in the shape of the boundary between the glabrous and strigose portions of the callus. In addition, A. nevadense is usually pubescent below the lower cauline nodes, and has paleas that are longer in relation to the lemmas. Plants of A. nevadense from Convict Creek Basin, California, are unusual in having culms that are glabrous below the lower nodes, but in other respects they correspond to A. nevadense. Achnatherum nevadense also resembles A. latiglume, but the latter species has blunter calluses and paleas that tend to be thicker and somewhat longer in comparison to the lemmas than those of A. nevadense.

 

5. Achnatherum occidentale (Thurb.) Barkworth

Plants tightly cespitose, not rhizomatous. Culms 14–120(180) cm tall, 0.3–2 mm thick, inter-nodes glabrous or puberulent to densely pubescent; nodes 2–4, glabrous or pubescent. Basal sheaths glabrous or puberulent to densely pubescent, often ciliate at the throat; collars often with tufts of hair at the sides; ligules 0.2–1.5 mm, often ciliate; blades 0.5–3 mm wide and flat, or convolute and 0.1–0.8 mm in diameter, lax to straight. Panicles 5–30 cm long, 0.5–1.5 cm wide; branches appressed, straight, longest branches 1–7 cm. Spikelets appressed to the branches. Glumes subequal, 9–15 mm long, 0.6–0.9 mm wide; florets 5.5–7.5 mm long, 0.5–0.9 mm thick, fusiform, terete; calluses 0.8–1.2 mm, sharp, dorsal boundary of the glabrous tip with the callus hairs narrowly acute; lemmas evenly hairy, hairs 0.5–1.5 mm at midlength, apical hairs somewhat longer than those below, sometimes similar in length to those at the base of the awns, sometimes longer, apical lobes 0.3–0.5 mm, membranous; awns 15–55 mm, twice-geniculate, first 2 segments evidently hairy, terminal segment glabrous or partly to wholly pilose, sometimes scabrous; paleas 2.2–3.5 mm, 2/5–3/5 as long as the lemmas, hairs at the tip usually shorter than 1 mm, frequently extending beyond the apices, apices rounded; anthers 2.5–3.5 mm, dehiscent, not penicillate. Caryopses 4–6 mm, fusiform. 2n = 36.

Achnatherum occidentale, which extends from British Columbia to California, Utah, and Colorado, varies considerably in pubescence and size. The three subspecies recognized here occasionally occur together.

1. Terminal awn segment usually pilose; culms 0.3–1 mm thick, glabrous even on the basal internodes; glumes often purplish ... subsp. occidentale
1. Terminal awn segment usually scabrous or glabrous, occasionally pilose at the base; culms 0.5–2 mm thick; glumes usually green ... 2
2. First 2 awn segments scabrous or pilose with hairs of mixed lengths; apical lemma hairs longer than the basal awn hairs ... subsp. californicum
2. First 2 awn segments pilose, the hairs gradually and evenly becoming shorter towards the first geniculation; apical lemma hairs similar in length to the basal awn hairs ... subsp. pubescens

 

Achnatherum occidentale subsp. californicum (Merr. & Burtt Davy) Barkworth
California Needlegrass

Culms 30–100(180) cm tall, 0.5–2 mm thick, internodes glabrous or pubescent, sometimes densely pubescent; nodes 2–4, glabrous or pubescent. Sheaths glabrous, pubescent, or pilose; collars usually with tufts of hair at the sides; blades 0.8–2 mm wide, usually erect or ascending, adaxial surfaces pilose. Panicles 8–30 cm; branches appressed, longest branches to 7 cm. Glumes usually green; lower glumes 0.6–0.8 mm wide; lemmas with hairs to 0.8 mm at midlength, apical hairs to 1.8 mm, longer than the basal awn hairs; awns 18–55 mm, scabrous or pilose on the first 2 segments, with hairs to 0.5 mm and of mixed lengths, terminal segment usually scabrous, occasionally pilose at the base. 2n = 36.

Achnatherum occidentale subsp. californicum grows from Washington through Idaho to southwestern Montana and south to California and Nevada, with disjunct records from south-central Wyoming and southwestern Utah. Its elevation range is 2000–4000 m.

Johnson (1962) postulated that Achnatherum occidentale subsp. californicum is a hybrid derivative of A. nelsonii and A. occidentale; it intergrades with both. The scattering of longer hairs among shorter hairs on the basal awn segments, combined with the long apical lemma hairs, give florets of subsp. californicum a more untidy appearance than those of the other two subspecies. It resembles A. nevadense in this respect, but differs from that species in the shape of the boundary between the glabrous and strigose portions of the callus, in usually being glabrous below the lower cauline nodes, and in having paleas that are shorter in relation to the lemmas. Plants with scabrous awns are often confused with A. nelsonii subsp. nelsonii; they differ in having sharper calluses, a more elongated extension of the glabrous callus area into the strigose portion of the callus, and, usually, longer awns.

 

Achnatherum occidentale (Thurb.) Barkworth subsp. occidentale
Western Needlegrass

Culms 14–50 cm tall, 0.3–1 mm thick, internodes glabrous. Basal sheaths mostly glabrous, often ciliate or sparsely tomentose at the throat; collars usually without tufts of hair at the sides; blades 0.3–2 mm wide when flat, usually convolute and 0.1–0.2 mm in diameter. Panicles 5–20 cm; longest branches 1.5–4 cm. Glumes often purplish; lemmas with apical pubescence similar in length to the basal awn pubescence; awns 15–42 mm, first 2 segments always pilose, terminal segment usually pilose, hairs becoming shorter distally, occasionally scabridulous or smooth.

Achnatherum occidentale subsp. occidentale grows above 2400 m, primarily in California. It differs from A. occidentale subsp. pubescens in having culms that are glabrous throughout and awns with terminal segments that are usually pilose. One specimen from Idaho has been seen; it has the palea/lemma ratio of subsp. californicum but the pilose terminal awn segments, slender habit, and purplish coloration of subsp. occidentale.

 

Achnatherum occidentale subsp. pubescens (Vasey) Barkworth
Common Western Needlegrass

Culms 32–120 cm tall, 0.8–1.3(2) mm thick, basal internodes puberulent to pubescent. Basal sheaths usually pubescent, sometimes densely pubescent, occasionally glabrous; collars often with tufts of hair at the sides; blades 1–3 mm wide, adaxial surfaces pubescent to pilose. Panicles 10–30 cm; longest branches 2–7 cm. Glumes usually green; lemmas with apical pubescence similar in length to the basal awn pubescence; awns 24–50 mm, pilose on the first 2 segments, with hairs gradually becoming shorter distally, terminal segment scabrous or glabrous. 2n = 36.

Achnatherum occidentale subsp. pubescens grows from Washington to California and eastward to Wyoming, at 1300–4700 m. It is the most widespread and variable subspecies of A. occidentale, intergrading with subsp. californicum, A. nelsonii, and A. lettermanii. It differs from the latter two in its shorter paleas and its pilose awns.

 

6. Achnatherum nelsonii (Scribn.) Barkworth

Plants cespitose, not rhizom-atous. Culms 40–175 cm tall, 0.7–2.4 mm thick, lower cauline internodes usually glabrous, sometimes slightly pubescent below the lower nodes; nodes 2–5. Basal sheaths glabrous or sparsely to densely pubescent, margins sometimes ciliate; collars glabrous or somewhat pubescent, without tufts of hair on the sides, collars of the flag leaves glabrous or sparsely pubescent; basal ligules 0.2–0.7 mm, membranous, truncate to rounded, usually not ciliate; upper ligules 1–1.5 mm, acute; blades (0.5)1.2–5 mm wide. Panicles 9–36 cm long, 0.8–2 cm wide; branches ascending to appressed, straight. Spikelets appressed to the branches. Glumes 6–12.5 mm long, 0.7–1.1 mm wide; lower glumes exceeding the upper glumes by 0.2–0.8 mm; florets 4.5–7 mm long, 0.6–0.9 mm thick, fusiform; calluses 0.2–1 mm, blunt to sharp, dorsal boundary of the glabrous tip with the callus hairs almost straight to acute; lemmas evenly hairy, hairs at midlength 0.5–1 mm, hairs at the apices to 2 mm, erect to ascending, apical lobes 0.1–0.4 mm, membranous, flexible; awns 19–45 mm, persistent, twice-geniculate, first 2 segments scabrous or with hairs shorter than 0.5 mm, terminal segment straight; paleas 2–4 mm, 1/3–2/3 as long as the lemmas, pubescent, hairs usually not exceeding the apices, veins terminating before the apices, apices rounded; anthers 2–3.5 mm, dehiscent, not penicillate. Caryopses 3–4 mm, fusiform. 2n = 36, 44.

Achnatherum nelsonii grows in meadows and openings, from sagebrush steppe and pinyon-juniper woodlands to subalpine forests, at 500–3500 m. It flowers in late spring to early summer, differing in this respect from A. perplexum. It is sometimes sympatric with A. lettermanii, from which it differs in its shorter paleas and wider leaves, and its tendency to grow in deeper or less disturbed soils. It differs from A. lemmonii in having wider leaf blades, shorter paleas, and membranous lemma lobes, and from A. nevadense and A. occidentale in its scabrous awns and the truncate to acute boundary of the glabrous tip of the callus with the callus hairs.

The two subspecies intergrade to some extent. There is also intergradation with Achnatherum occidentale, possibly as a result of hybridization and introgression.

1. Calluses blunt, dorsal boundary of the glabrous tip and the callus hairs almost straight to rounded; awns 19–31 mm long ... subsp. dorei
1. Calluses sharp, dorsal boundary of the glabrous tip and the callus hairs acute; awns 19–45 mm long ... subsp. nelsonii

 

Achnatherum nelsonii subsp. dorei (Barkworth & J.R. Maze) Barkworth
Dore’s Needlegrass

Calluses blunt, glabrous tips 0.02–0.06 mm, dorsal boundary of the glabrous tip and the callus hairs almost straight to rounded; awns 19–31 mm.

Achnatherum nelsonii subsp. dorei grows from the southern Yukon Territory to California and Wyoming. In regions where both subspecies grow, subsp. dorei is at higher elevations than subsp. nelsonii. It differs from A. robustum in the sparsely hairy collars of its flag leaves.

Reports of Achnatherum nelsonii subsp. dorei (identified as Stipa columbiana Macoun by many authors) from New Mexico and Arizona are probably based on A. perplexum, which differs in having sparse, narrow inflorescences and slightly recurved glumes. The two also differ in flowering time, A. nelsonii subsp. dorei flowering in late spring to early summer and A. perplexum in the fall. Achnatherum nelsonii subsp. nelsonii is present in New Mexico. Scagel and Maze (1984) concluded that putative hybrids between A. nelsonii subsp. dorei and A. richardsonii were merely large plants of A. nelsonii subsp. dorei that varied in the direction of A. richardsonii.

 

Achnatherum nelsonii (Scribn.) Barkworth subsp. nelsonii
Nelson’s Needlegrass

Calluses sharp, acute to acuminate, glabrous tips 0.05–0.15 mm, dorsal boundary of the glabrous tip and the callus hairs acute; awns 19–45 mm.

Achnatherum nelsonii subsp. nelsonii intergrades with subsp. dorei in Montana and Wyoming, and with A. occidentale subsp. pubescens in California. Its range extends from Idaho and Montana south to Nevada. It tends to grow at lower elevations than subsp. dorei.

 

7. Achnatherum latiglume (Swallen) Barkworth
Wide-Glumed Needlegrass

Plants tightly cespitose, not rhizomatous. Culms 50–110 cm tall, 0.7–1.2 mm thick, lower internodes retrorsely pilose, upper internodes glabrous; nodes 2–4. Basal sheaths usually retrorsely pubescent, brown to gray-brown, flat when mature; collars usually glabrous, some-times with a few hairs at the sides; basal ligules 0.2–2.5 mm, truncate to rounded; upper ligules 1.2–3 mm, rounded to acute, ciliate; blades 0.7–3 mm wide, straight to lax, abaxial surfaces smooth, glabrous, adaxial surfaces pubescent, scabrous. Panicles 15–30 cm long, 0.8–2 cm wide; branches appressed to strongly ascending, longest branches 2.5–6.5 cm. Glumes subequal, 12–15 mm long, 1.3–1.9 mm wide, 3-veined; florets 8–9 mm long, 0.9–1.4 mm thick, fusiform, terete; calluses 0.7–1 mm, blunt to sharp; lemmas evenly hairy, hairs 0.5–1.5 mm at midlength, apical hairs 1–2 mm, apical lobes to 1 mm, membranous; awns 33–45 mm, persistent, twice-geniculate, first 2 segments pilose, with hairs 0.5–2 mm, terminal segment mostly scabrous, straight; paleas 4–5 mm, 3/5–4/5 as long as the lemmas, pubescent; anthers not seen. Caryopses not seen. 2n = 70.

Achnatherum latiglume usually grows on dry slopes in yellow pine forests of southern California. Pohl (1954) demonstrated that it is an alloploid derivative of A. nelsonii and A. lemmonii. He reported being told that it was a fairly common species in the Yosemite Valley, and suggested that the isolated occurrences in Riverside and Fresno counties might represent separate origins of the species.

Achnatherum latiglume resembles A. nevadense and A. occidentale, but the latter two species have sharper calluses, and their paleas tend to be thinner and somewhat shorter relative to the lemmas than those of A. latiglume.

 

8. Achnatherum lemmonii (Vasey) Barkworth
Lemmon’s Needlegrass

Plants tightly cespitose, not rhizomatous. Culms 15–90 cm tall, 0.7–1 mm thick, glabrous, pubescent, or tomentose; nodes 3–4. Basal sheaths glabrous, pubescent, or tomentose; collars, including the sides, glabrous or sparsely pubescent, hairs shorter than 0.5 mm; basal ligules 0.5–1.2 mm, hyaline, glabrous, truncate to acute; upper ligules to 2.5 mm; basal blades 0.5–1.5 mm wide, folded to convolute, abaxial surfaces smooth, glabrous, adaxial surfaces prominently ribbed, often with 0.3–0.5 mm hairs, sometimes glabrous; upper blades to 2.5 mm wide, otherwise similar to the basal blades. Panicles 7–21 cm long, about 1 cm wide; branches straight, strongly ascending to appressed, longest branches 4–5 cm. Spikelets appressed to the branches. Glumes subequal, 7–11.5 mm; lower glumes 0.9–1.1 mm wide, 4–5-veined; upper glumes 3-veined; florets 5.5–7 mm long, 0.8–1.3 mm thick, fusiform, somewhat laterally compressed; calluses 0.4–1.2 mm, blunt; lemmas coriaceous, evenly pubescent, hairs 0.4–1 mm, apices 1-lobed, lobe about 0.1 mm long, thick, stiff, apical lemma hairs 0.4–0.8 mm; awns 16–30 mm, persistent, (once)twice-geniculate, all segments scab-rous, terminal segment straight; paleas 4.5–6.5 mm, from 3/4 as long as to equaling the lemmas, sparsely to moderately pubescent, hairs not exceeding the apices, veins terminating below the apices, apices flat or pinched; anthers 2.3–3.5 mm, dehiscent, not penicillate. Caryopses 4–5 mm, fusiform. 2n = 34.

Achnatherum lemmonii grows in sagebrush and yellow pine associations, from southern British Columbia to California and east to Utah. It has been confused in the past with A. nelsonii; it differs in having narrower leaves, laterally compressed florets with a thick apical lobe, and longer paleas.

1. Lower sheaths and culms glabrous or pubescent, not tomentose, the hairs to 0.2 mm long ... subsp. lemmonii
1. Lower sheaths and culms tomentose, the hairs 0.4–0.6 mm long ... subsp. pubescens

 

Achnatherum lemmonii (Vasey) Barkworth subsp. lemmonii

Sheaths and culms glabrous or pubescent, hairs to 0.2 mm, sometimes varying within a population.

Achnatherum lemmonii subsp. lemmonii grows throughout the range shown on the map, on both serpentine and non-serpentine soils.

 

Achnatherum lemmonii subsp. pubescens (Crampton) Barkworth

Lower sheaths and culms densely tomentose, hairs 0.4–0.6 mm.

Achnatherum lemmonii subsp. pubescens is restricted to serpentine soils in southern California. Barkworth and Linman (1984) rejected subsp. pubescens, not appreciating that it differed in having tomentose, rather than pubescent, culms.

 

9. Achnatherum thurberianum (Piper) Barkworth
Thurber’s Needlegrass

Plants cespitose, not rhizom-atous. Culms 30–75 cm tall, 0.5–1.7 mm thick, internodes pubescent or glabrous, pub-escence more common on the lower internodes, particularly just below the nodes; nodes 2–3, lower nodes retrorsely pubescent, upper nodes glab-rous or pubescent. Basal sheaths glabrous, usually smooth, brown or gray-brown; collars glabrous, without tufts of hair at the sides; basal ligules 1.5–6 mm, hyaline, rounded to acute, lacerate; upper ligules to 8 mm, hyaline, acute, glabrous; blades 0.5–2 mm wide, convolute, abaxial surfaces scabrous, adaxial surfaces scabrous or hairy, hairs about 0.3 mm. Panicles 7–15 cm long, 0.5–2.5 cm wide, often included in the upper leaf sheaths at the start of anthesis; branches 1.5–6 cm, appressed to strongly ascending, with 1–6 spikelets. Glumes often purplish; lower glumes 10–15 mm long, 1.2–2 mm wide; upper glumes to 2 mm shorter; florets 6–9 mm long, 0.7–1.2 mm thick, fusiform, terete; calluses 0.9–1.5 mm, sharp; lemmas coriaceous, evenly pubescent or the back glabrate distally, hairs 0.5–0.8 mm, apices lobed on 1 margin, lobe about 0.1 mm long, thick, apical lemma hairs 0.5–0.8 mm; awns 32–56 mm, twice-geniculate, first 2 segments pilose, hairs 0.8–2 mm, terminal segment glabrous, often scabrous; paleas 4.6–6.1 mm, 3/4–9/10 as long as the lemmas, sparsely pubescent towards the base; anthers 2.5–3.5 mm, dehiscent, not penicillate. Caryopses 5–7 mm, fusiform. 2n = 34.

Achnatherum thurberianum grows in canyons and foothills, primarily in sagebrush desert and juniper woodland associations, from Washington to southern Idaho and southwestern Montana and from California to Utah, at 900–3000 m. Its long ligules and pilose awns make it one of the easier North American species of Achnatherum to identify.

 

10. Achnatherum coronatum (Thurb.) Barkworth
Crested Needlegrass

Plants loosely cespitose, shortly rhizomatous, bases knotty. Culms 55–210 cm tall, 3–6 mm thick, internodes usually glab-rous, lower internodes some-times puberulent; nodes 1–2, glabrous. Basal sheaths mostly glabrous, often puberulent on the lower portion, flat, ribbon-like with age, margins hairy distally, hairs 1–2.5 mm; collars mostly glabrous; ligules 0.4–1.6(3) mm, truncate to slightly rounded, abaxial surfaces pubescent, ciliate, cilia about 0.5 mm; blades usually flat, 2.5–7 mm wide, both surfaces scabrous. Panicles 15–60 cm long, 2–4 cm wide; branches widely spreading to ascending, longest branches 4–13 cm. Glumes lanceolate, glabrous, tapering to awnlike apices; lower glumes 16–21 mm long, 1–1.3 mm wide, midveins scabrous; upper glumes 11–18 mm; florets 6.5–10 mm long, about 1 mm thick, fusiform, terete; calluses 0.5–2 mm, blunt to acute; lemmas densely hairy, hairs at midlength 1.5–4 mm, apical hairs 2–5 mm; awns 25–45 mm, persistent, twice-geniculate, all segments scabrous, terminal segment straight; paleas 3.5–5.5 mm, 3/5–9/10 as long as the lemmas, sparsely hairy between the veins, apices flat, rounded; anthers 3–4 mm, dehiscent, not penicillate. Caryopses 5–7 mm, fusiform. 2n = 40.

Achnatherum coronatum grows on gravel and on rocky slopes, mostly in chaparral associations of the Coast Range from Monterey County, California, to Baja California, Mexico. It is similar in size to A. diegoense, but differs in its mostly glabrous internodes and longer paleas. It differs from A. parishii, an inland species, in its twice-geniculate awns, more robust habit, and more sparsely pubescent paleas. Occasional plants combine the characteristics of both species.

 

11. Achnatherum parishii (Vasey) Barkworth

Plants tightly cespitose, not rhizomatous. Culms 14–80 cm tall, 0.8–2 mm thick, internodes glabrous or pubescent below the nodes; nodes 3–5, glabrous. Basal sheaths mostly glabrous, sometimes pubescent at the base, flat and ribbonlike with age, margins sometimes hairy distally, hairs adjacent to the ligules 0.5–3 mm; collars glabrous; ligules truncate, abaxial surfaces pubescent, ciliate, cilia as long as or longer than the basal membrane, ligules of basal leaves 0.3–0.8 mm, of upper leaves 0.5–1.5 mm, asymmetric; blades 4–30+ cm long, 1–4.2 mm wide, usually flat and more or less straight, sometimes tightly convolute and arcuate. Panicles 7–15 cm long, 1.5–4 cm wide; branches strongly ascending at maturity, longest branches 1.5–4 cm. Glumes unequal to subequal, narrowly lanceolate, 3–5-veined; lower glumes 9–15 mm long, 0.9–1.2 mm wide; upper glumes 8–15 mm; florets 4.8–6.5 mm long, 0.8–1 mm thick, fusiform, terete; calluses 0.2–0.8 mm, acute; lemmas evenly and densely hairy, hairs 1.5–3.5 mm at midlength, apical hairs 2.5–5 mm; awns 10–35 mm, persistent, once-geniculate, first segment scabrous or strigose, hairs to 0.3 mm, terminal segment straight; paleas 2.5–4.5 mm, 1/2–4/5 times the length of the lemmas, hairy between the veins, hairs often as long as those on the lemmas but not as dense, apices usually rounded, occasionally somewhat pinched; anthers 2.3–4.5 mm, dehiscent, not penicillate. Caryopses 3–6 mm, fusiform. 2n = unknown.

Achnatherum parishii grows from the coastal ranges of California to Nevada and Utah, south to Baja California, Mexico, and to the Grand Canyon in Arizona. It differs from A. coronatum in its once-geniculate awns, more densely pubescent paleas, and generally smaller stature; from A. scribneri in its shorter, blunter calluses and more abundant lemma hairs; and from A. perplexum in having longer hairs on its lemmas.

1. Basal sheath margins glabrous or hairy distally, hairs to 0.5 mm long; culms 14–35 cm tall ... subsp. depauperatum
1. Basal sheath margins hairy distally, hairs 1–3.2 mm long; culms 20–80 cm tall ... subsp. parishii

 

Achnatherum parishii subsp. depauperatum (M.E. Jones) Barkworth
Low Needlegrass

Culms 14–35 cm tall, 0.8–1.7 mm thick, glabrous. Basal sheath margins glabrous or hairy distally, hairs to 0.5 mm; blades 4–15 cm long, 1–2.5 mm wide, usually 0.5–1.5 mm in diameter and tightly convolute, conspicuously arcuate distally, abaxial surfaces smooth, glabrous, adaxial surfaces scabrous. Panicles 7–12 cm long, 1.5–2.5 cm wide. Florets 4.8–6 mm; paleas densely hairy between the veins, some hairs as long as those on the lemmas; awns 10–17 mm; anthers 2.3–2.8 mm. Caryopses 3–4 mm, fusiform. 2n = unknown.

Achnatherum parishii subsp. depauperatum grows in gravel and on rocky slopes, in juniper and mixed desert shrub associations, from central Nevada to western Utah. It differs from A. webberi in its persistent awns and thicker leaves that tend to curl when dry, and from A. parishii subsp. parishii in its smaller stature, glabrous or shortly hairy sheath margins, and densely hairy paleas.

 

Achnatherum parishii (Vasey) Barkworth subsp. parishii
Parish’s Needlegrass

Culms 20–80 cm tall, 1.5–2 mm thick, mostly glabrous, pubescent below the nodes. Basal sheath margins hairy distally, hairs 1–3.2 mm; blades 11–30+ cm long, 2.5–4.2 mm wide, usually flat or only partly closed, sometimes completely convolute, straight to somewhat arcuate distally. Panicles 11–15 cm long, 2–4 cm wide. Florets 5.5–6.5 mm; awns 15–35 mm; paleas sparsely hairy between the veins, hairs about 1/2 as long as the lemma hairs, apices usually rounded, occasionally somewhat pinched; anthers 3.5–4.5 mm, glabrous. Caryopses 5–6 mm, fusiform. 2n = unknown.

Achnatherum parishii subsp. parishii grows on dry, rocky slopes, in desert shrub and pinyon-juniper associations, from the coastal ranges of California to northeastern Nevada, eastern Utah, and the Grand Canyon in Arizona. Its range extends into Baja California, Mexico. It differs from A. coronatum in its shorter culms and once-geniculate awns, and from subsp. depauperatum in its longer culms, hairy sheath margins, and sparsely hairy paleas.

 

12. Achnatherum robustum (Vasey) Barkworth
Sleepygrass

Plants cespitose, not rhizom-atous. Culms 100–230 cm tall, 2–4.5 mm thick, mostly glabrous, often pubescent below the nodes, the pub-escence antrorse or retrorse; nodes 4–5. Basal sheaths mostly glabrous, margins usually ciliate distally; collars hairy, those of the flag leaves densely hairy, hairs 0.5–2 mm, sides glabrous; basal ligules 1–2 mm; upper ligules to 4 mm, truncate, rounded, or obtuse, glabrous; blades 6–10 mm wide, glabrous, abaxial surfaces smooth, adaxial surfaces prominently ribbed, ribs scabrous. Panicles 15–30 cm long, 0.8–3.5 cm wide; branches straight, appressed to ascending, lower branches 3–9 cm. Spikelets appressed to the branches. Glumes subequal, 9–11.5 mm long, 1–1.4 mm wide; florets 5.9–8.5 mm long, 0.9–1.2 mm thick, fusiform, terete; calluses 0.3–1 mm, blunt; lemmas evenly hairy, hairs at midlength 0.3–0.8 mm, apical hairs to 1.5 mm; awns 20–32 mm, persistent, twice-geniculate, scabridulous to scabrous, scabrules to about 0.1 mm, longest on the middle segment, terminal segment straight; paleas 3.7–5.6 mm, 2/3–3/4 as long as the lemmas, hairy, hairs about 0.5 mm, not exceeding the apices, veins terminating below the apices, apices rounded; anthers 4–5 mm, dehiscent, penicillate. Caryopses 5–6 mm. 2n = 64.

Achnatherum robustum grows on dry plains and hills, in open woods and forest clearings, and along roadsides, from Wyoming through Colorado to Arizona, New Mexico, and northern Mexico. Records from Kansas represent recent introductions; it is not clear whether the species has persisted there. Achnatherum robustum is sometimes confused with A. nelsonii subsp. dorei and Nassella viridula; it differs from both in the densely hairy collars of its flag leaves. Although not widely available, it has potential as an ornamental grass, particularly in arid regions with cold winters.

The English-language name refers to the effect some samples, particularly those from the Sacramento and Sierra Blanca mountains, New Mexico, have on livestock, especially horses and cattle. “Mildly poisoned animals are dejected, inactive, and withdrawn; severely poisoned animals lie on their sides in a profound slumber” (Cheeke and Shull 1985). The active ingredient is diacetone alcohol (Epstein et al. 1964).

 

13. Achnatherum diegoense (Swallen) Barkworth
San Diego Needlegrass

Plants cespitose, not rhizom-atous. Culms 110–140 cm tall, 2.5–4 mm thick, internodes densely and retrorsely pub-escent for 3–9 mm below the nodes, particularly the lower nodes, glabrous or retrorsely puberulent elsewhere; nodes 3, pubescent or glabrate. Basal sheaths mostly glabrous or puberulent, margins ciliate distally; collars glabrous or with hairs, hairs mostly to 0.5 mm, sides with tufts of 1.5–2 mm hairs; ligules 0.4–2 mm, rounded to acute, abaxial surfaces hairy, hairs to 0.5 mm; upper ligules 1–3 mm, similar in structure and pubescence; blades 1–3.5 mm wide, abaxial surfaces smooth or scabrous, adaxial surfaces prominently ribbed, hairy, hairs 2–3 mm. Panicles 21–25 cm long, (2)4–8 cm wide; branches strongly divergent to ascending, straight, lower branches 5–7 cm. Spikelets appressed to the branches. Glumes subequal, 8–11.5 mm; lower glumes 0.5–1 mm wide, 3–5-veined; upper glumes 3-veined; florets 5.5–7.5 mm long, 0.7–1 mm thick, fusiform, terete; calluses 0.25–1.2 mm, acute; lemmas evenly hairy, hairs at midlength and at the apices 0.5–1 mm, apical lobes 0.2–0.4 mm, membranous, flexible; awns 20–50 mm, persistent, twice-geniculate, all segments scabrous to scabridulous, terminal segment straight; paleas 2.6–3.8 mm, 1/2–3/4 as long as the lemmas, pubescent, hairs not extending beyond the apices, veins terminating below the apices, apices rounded; anthers 2.5–4 mm, dehiscent, not penicillate. 2n = unknown.

Achnatherum diegoense grows in chaparral and coastal sage scrub, on rocky soil near streams or the coast, at 0–350 m, on the Channel Islands of Santa Barbara County, California, and, on the mainland, in Ventura and San Diego counties south into Baja California, Mexico.

 

14. Achnatherum lobatum (Swallen) Barkworth
Lobed Needlegrass

Plants cespitose, not rhizom-atous. Culms 40–100 cm tall, 0.6–2.6 mm thick, glabrous or sparsely pubescent to 5 mm below the lower nodes; nodes 4. Basal sheaths becoming flat and papery in age, margins some-times ciliate distally, cilia to 0.5 mm; collars, including the sides, glabrous or sparsely pubescent, collars of the flag leaves glabrous; basal ligules 0.2–1.3 mm, membranous, truncate, erose to ciliate, cilia about 0.05 mm; upper ligules 0.3–1 mm; blades 1–4 mm wide, abaxial surfaces smooth, adaxial surfaces scabrous. Panicles 12–28 cm long, 0.5–1.5 cm wide; branches ascending to appressed, straight, longest branches 3–6 cm. Spikelets appressed to the branches. Glumes unequal; lower glumes 9.5–12.5 mm long, 0.8–1.2 mm wide, 3(5, 7)-veined, apices straight to somewhat recurved; upper glumes 2–3.5 mm shorter, 3-veined; florets 5.5–7.5 mm long, 0.6–1.1 mm thick, terete, widest about midlength; calluses 0.3–0.5 mm, blunt; lemmas evenly hairy, hairs at midlength 0.7–1.2 mm, fusiform, terete, apical hairs 1.3–2.2 mm, erect, usually less than 1 mm longer than those at midlength, apical lobes 0.5–1.2 mm, membranous, flexible; awns 10–22 mm, persistent, once- or twice-geniculate, scabrous, terminal segments straight; paleas 3–4.3 mm, 3/5–3/4 as long as the lemmas, pubescent, hairs exceeding the apices, veins terminating below the apices, apices flat, rounded; anthers 3–4 mm, dehiscent, sparsely penicillate, hairs about 0.1 mm. 2n = unknown.

Achnatherum lobatum grows on rocky, open slopes in pinyon-pine and white fir associations of southern Arizona, New Mexico, Texas, and northern Mexico, at 2100–2800 m. It flowers from mid- to late summer.

Achnatherum lobatum is similar to A. scribneri and A. perplexum. It differs from A. scribneri in its shorter apical lemma hairs and blunt calluses, and from A. perplexum in having longer lemma lobes and erect apical hairs.

 

15. Achnatherum aridum (M.E. Jones) Barkworth
Mormon Needlegrass

Plants cespitose, not rhizom-atous. Culms 35–85 cm tall, 0.9–2.5 mm thick, usually glabrous and smooth, some-times scabridulous or puber-ulent; nodes 2–3. Basal sheaths glabrous, upper sheath margins hyaline distally; collars of th. Basal sheaths occasionally with a small tuft of 0.8 mm hair on the sides, collars of the upper leaves glabrous, scabridulous, or sparsely puberulent; ligules 0.2–1.5 mm, truncate to rounded, erose, sometimes ciliate, cilia about 0.05 mm; blades 0.9–3 mm wide, abaxial surfaces smooth or scabridulous, glabrous, adaxial surfaces hirtellous, hairs to 0.5 mm. Panicles 5–17 cm long, 1–1.5 cm wide, contracted, bases often enclosed at anthesis; branches appressed or strongly ascending, straight, lower branches 1.5–4 cm. Lower glumes 8–15 mm long, 0.6–0.8 mm wide; upper glumes 1–5 mm shorter; florets 4–6.5 mm long, 0.6–1.1 mm thick, fusiform, terete; calluses 0.2–1 mm, sharp; lemmas evenly hairy on the lower portion, hairs 0.2–0.5 mm, the distal 1/5–1/4 often glabrous, apical hairs absent or fewer than 5, to 1.5 mm; awns 40–80 mm, persistent, obscurely once-geniculate, scabridulous, terminal segment flexuous; paleas 2–3.2 mm, 1/2–3/4 as long as the lemmas, pubescent, hairs exceeding the apices, apices rounded, flat; anthers 2–3.5 mm, dehiscent, not penicillate. 2n = unknown.

Achnatherum aridum grows on rocky outcrops, in shrub-steppe and pinyon-juniper associations, from southeastern California to Colorado and New Mexico, at 1200–2000 m. It has also been reported from Texas, but no specimens documenting these reports have been located. It has not been found in Mexico.

 

16. Achnatherum eminens (Cav.) Barkworth
Southwestern Needlegrass

Plants cespitose, shortly rhi-zomatous, bases knotty. Culms 50–100 cm tall, 0.8–1.5 mm thick, glabrous; nodes 2–3. Basal sheaths mostly glabrous, ciliate on the margins; collars glabrous on the back, usually with tufts of hair on the sides, hairs about 0.8 mm; basal ligules 0.8–1.6 mm, membranous, glabrous, rounded to acute; upper ligules to 4.5 mm, acute; blades 0.7–3.5 mm wide, abaxial surfaces smooth to scabridulous, adaxial surfaces prominently ribbed, scabridulous or sparsely to densely pubescent, hairs about 0.1 mm. Panicles 20–55 cm long, 3–8 cm wide, open, often enclosed to midlength at anthesis; lower branches 5–8 cm, ascending to divergent, flexuous. Lower glumes 5–12 mm long, 0.5–0.7 mm wide, 3–5-veined; upper glumes 1–4 mm shorter, 3-veined; florets 4–7.5 mm long, 0.5–0.9 mm thick, fusiform, terete; calluses 1–2 mm, sharp; lemmas evenly hairy, hairs 0.4–0.8 mm throughout, apical lobes not present; awns 35–70 mm, persistent, twice-geniculate, first 2 segments scabrous, terminal segment flexuous; paleas 1–2 mm, 1/3–1/2 as long as the lemmas, sparsely to moderately pubescent, apices rounded, flat; anthers 3–3.5 mm, dehiscent, a few penicillate, hairs about 0.3 mm. Caryopses about 4 mm, fusiform. 2n = 44, 46.

Achnatherum eminens grows on dry, rocky slopes and valleys in the mountains of the southwestern United States, primarily in desert scrub, at 600–2600 m. Its range extends into Mexico. It is easy to recognize because of its open panicle, flexuous branches, and flexuous awns. It is superficially similar to Nassella cernua, but differs in its longer, glabrous ligules, not or weakly overlapping lemma margins, pubescent paleas, and geographic distribution.

 

17. Achnatherum richardsonii (Link) Barkworth
Richardson’s Needlegrass

Plants tightly cespitose, not rhizomatous. Culms 30–100 cm tall, 1–1.5 mm thick, glabrous; nodes usually 3. Basal sheaths glabrous, margins ciliolate; collars glabrous, without tufts of hair on the sides; ligules 0.1–0.5 mm, truncate, ciliolate; blades 0.8–3 mm wide, convolute when dry, abaxial surfaces scabridulous, adaxial surfaces glabrous. Panicles 7–25 cm long, 7–15 cm wide; branches divergent, flexuous, longest branches 7–10 cm, with the spikelets confined to the distal 1/4. Spikelets pendulous. Lower glumes 7.5–11 mm long, 0.9–1.2 mm wide; upper glumes 2–3 mm shorter; florets 5–6 mm long, 0.6–0.9 mm thick, fusiform, terete; calluses 0.4–0.7 mm, blunt; lemmas evenly hairy on the lower portion, often glabrate distally, body and apical hairs 0.2–0.5 mm, apical lobes not or scarcely developed, to 0.1 mm; awns 15–25 mm, persistent, twice-geniculate, first 2 segments strigulose, hairs about 0.1 mm, terminal segment straight; paleas 2.2–3.6 mm, 1/2–3/5 as long as the lemmas, pubescent, hairs not exceeding the apices, apices rounded; anthers 2.5–3 mm, dehiscent, penicillate, hairs 0.1–0.5 mm. Caryopses 3–4 mm, fusiform. 2n = 44.

Achnatherum richardsonii grows in open woodlands and grasslands, often on sand or gravel, from the Yukon Territory to Washington and Manitoba, and south in the Rocky Mountains through Montana and Wyoming to western South Dakota and northern Colorado. Its elevation range is 1000–3100 m. It is readily recognized by its combination of flexuous panicle branches, drooping spikelets, and straight distal awn segments. Scagel and Maze (1984) concluded that putative hybrids between A. richardsonii and A. nelsonii subsp. dorei were merely large plants of subsp. dorei that varied in the direction of A. richardsonii.

 

18. Achnatherum curvifolium (Swallen) Barkworth
Curlyleaf Needlegrass

Plants tightly cespitose, not rhizomatous. Culms 25–55 cm tall, 0.7–1 mm thick, glabrous; nodes 3. Basal sheaths usually puberulent, hairs 0.1–0.2 mm, sometimes densely tomentose at the base, brown to gray-brown when old; collars glabrous, sometimes with tufts of hair on the sides, hairs to 0.5 mm; ligules truncate, pubescent, hairs about 0.1; basal ligules about 0.3 mm, upper ligules to 0.6 mm; blades normally valvate to involute, about 0.5 mm in diameter, strongly arcuate, abaxial surfaces pubescent near the base, glabrous and smooth distally, adaxial surfaces densely hairy, hairs to 0.2 mm. Panicles 7–11 cm long, 1–2 cm wide; branches appressed to strongly ascending, longest branches 3–4 cm. Glumes subequal, 10–14 mm long, 0.7–0.9 mm wide; florets 6–8 mm long, 0.4–0.8 mm thick, fusiform, terete; calluses 1–1.5 mm, sharp; lemmas evenly hairy, hairs at midlength 0.3–1 mm, apical hairs 1–1.5 mm, apical lobes not developed; awns 22–38 mm, once-geniculate, first segment pubescent, hairs 1–2 mm, gradually decreasing in length distally; paleas 2–2.3 mm, 1/4–1/3 as long as the lemmas, glabrous; anthers about 3.5 mm, dehiscent, not penicillate. Caryopses about 4 mm, fusiform. 2n = 44.

Achnatherum curvifolium grows on cliffs and in disturbed, rocky, limestone habitats. It is known from relatively few locations in the Flora region; it is more common in northern Mexico. It is most readily distinguished from other species of Achnatherum in the Flora region by its combination of curly leaves and hairy awns.

 

19. Achnatherum scribneri (Vasey) Barkworth
Scribner’s Needlegrass

Plants cespitose, not rhizom-atous. Culms 25–90 cm tall, 0.5–1.6 mm thick, glabrous; nodes 3. Basal sheaths becom-ing flat and papery, margins ciliate distally; collars glabrous, with tufts of hair on the sides, hairs on the basal leaves to 1.5 mm, hairs on the flag leaves 1–2.5 mm; basal ligules 0.3–0.8 mm, truncate, erose, ciliate, cilia 0.2–0.4 mm; upper ligules to 1.5 mm, asymmetric, obliquely truncate for most of their width, abruptly longer on 1 side; blades to 30 cm long, 2–5 mm wide, flat or involute, long-tapering. Panicles 7–21 cm long, 0.5–1 cm wide; branches appressed to ascending, straight. Lower glumes 10–17 mm long, 0.7–1.2 mm wide, exceeding the upper glumes by 2.5–4.5 mm, apices tapering, often slightly recurved; florets 6–9.5 mm long, 0.6–1.1 mm thick, fusiform, terete, widest at or below midlength; calluses 0.5–1.5 mm, sharp; lemmas evenly hairy, hairs at midlength to 1 mm, apical hairs 2–3 mm, ascending, apical lobes 0.3–0.5 mm; awns 13–25 mm, persistent, usually once-geniculate, first segment scabrous, terminal segment straight; paleas 2.5–3.5 mm, 1/3–1/2 as long as the lemmas, pubescent, hairs not exceeding the apices, apices rounded; anthers 3–5 mm, dehiscent, not penicillate. Caryopses 5–6 mm, fusiform. 2n = 40.

Achnatherum scribneri grows on rocky slopes, in pinyon-juniper and ponderosa pine associations at 1500–2700 m, from southeastern Wyoming through Colorado to Arizona, New Mexico, western Oklahoma, and Texas, and in Capital Reef National Park, Utah. At present, the Utah population appears to be disjunct from the species’ primary range; this may reflect a lack of collecting. Achnatherum scribneri is similar to A. parishii, A. robustum, A. perplexum, and A. lobatum, differing from all of them in its sharp calluses.

 

20. Achnatherum perplexum Hoge & Barkworth
Perplexing Needlegrass

Plants cespitose, not rhizom-atous. Culms 35–90 cm tall, 0.7–2.2 mm thick, lower internodes glabrous, puberulent to 5 mm below the nodes; nodes 2–3. Basal sheaths mostly glab-rous, margins ciliolate distally; collars glabrous, including the sides; basal ligules 0.2–0.5 mm, truncate, ciliolate, cilia to 0.1 mm; upper ligules 0.2–3.5 mm, rounded to acute; blades to 30 cm long, 1–3 mm wide. Panicles 10–25 cm long, 0.5–1.5 cm wide; branches ascending to appressed, straight. Spikelets appressed to the branches. Glumes unequal; lower glumes 10–15 mm long, 0.5–1.1 mm wide, exceeding the upper glumes by 1–3(4) mm; florets 5.5–11 mm long, 0.7–1 mm thick, fusiform, terete, widest at or below midlength; calluses 0.4–0.6 mm, blunt; lemmas evenly hairy, hairs at midlength about 1 mm, apical hairs 1–2 mm, ascending to divergent, apical lobes 0.2–0.5 mm, membranous, flexible; awns 10–19 mm, persistent, once(twice)-geniculate, basal segments scabrous, terminal segments straight; paleas 2.8–5.6 mm, 1/2–2/3 as long as the lemmas, hairy, hairs not or scarcely exceeding the apices, veins terminating at or before the apices, apices acute to rounded; anthers 2.5–4 mm, dehiscent, not penicillate. Caryopses 3–6 mm, fusiform. 2n = unknown.

Achnatherum perplexum grows on slopes in pinyon-pine associations of the southwestern United States and adjacent Mexico, at 1500–1700 m. It flowers in late summer to early fall. It has generally been confused with A. scribneri, A. nelsonii, and A. lobatum. It differs from A. scribneri in the glabrous collar margins of its basal leaves and its blunt calluses; from A. nelsonii and A. lettermanii in its unequal glumes; from A. lettermanii in its relatively short paleas; and from A. lobatum in its shorter lemma lobes and ascending to divergent apical lemma hairs.

 

21. Achnatherum pinetorum (M.E. Jones) Barkworth
Pinewoods Needlegrass

Plants tightly cespitose, not rhizomatous. Culms 14–50(80) cm tall, 0.4–0.9 mm thick, mostly glabrous, lower inter-nodes often puberulent or pubescent, particularly below the nodes; nodes 2–3. Basal sheaths not becoming flat and ribbonlike with age, usually glabrous, throat sometimes with a few hairs, hairs about 0.2 mm; collars glabrous, including the sides; basal ligules 0.2–0.8 mm, truncate to rounded, membranous, glabrous; upper ligules to 2 mm, rounded; blades usually involute and 0.2–0.4 mm in diameter, 0.5–1 mm wide if flat, often arcuate distally, abaxial surfaces scabridulous, adaxial surfaces hairy, hairs about 0.1 mm. Panicles 4.5–20 cm long, 0.5–1 cm wide, contracted; branches appressed, lower branches 1–5 cm, with 2–7 spikelets. Glumes subequal, 7–11 mm long, 0.6–0.9 mm wide, lanceolate, not saccate; florets 3.5–5.5 mm long, 0.6–0.8 mm thick, fusiform, terete; calluses 0.4–0.6 mm, sharp; lemmas densely and evenly pilose, hairs at midlength 1.5–3.5 mm, apical hairs to 5 mm, apical lobes 0.3–2 mm, thin; awns 13–25 mm, persistent, twice-geniculate, first 2 segments scabrous; paleas 2.5–4 mm, from 2/3 as long as to equaling the lemmas, hairy; anthers 1.8–2.6 mm, dehiscent, not penicillate. Caryopses 2.5–4 mm, fusiform. 2n = 32.

Achnatherum pinetorum usually grows on rocky soil, in pinyon-juniper to subalpine associations, at 2100–3300 m. Its range extends from Oregon, Idaho, and Montana south to California, Nevada, and Colorado. It differs from A. webberi in its longer, persistent awns, and from A. lettermanii in its sharp calluses and longer lemma hairs.

 

22. Achnatherum webberi (Thurb.) Barkworth
Webber’s Needlegrass

Plants tightly cespitose, not rhizomatous. Culms 12–35 cm tall, 0.4–0.7 mm thick, smooth or antrorsely scabridulous; nodes 2–3. Basal sheaths glab-rous, smooth or scabridulous; collars glabrous, without tufts of hair on the sides; basal ligules 0.1–1 mm, truncate to rounded; upper ligules 1–2 mm, acute; blades 0.5–1.5 mm wide when flat, usually folded to involute and about 0.5 mm in diameter, stiff, abaxial surfaces smooth or scabrous, adaxial surfaces scabrous. Panicles 2.5–7 cm long, 0.5–2 cm wide, contracted; branches appressed, longest branches 1–2 cm. Glumes subequal, 6–10 mm long, 0.6–0.9 mm wide, lanceolate, not saccate; florets 4.5–6 mm long, 0.7–1 mm thick, fusiform, terete; calluses 0.3–0.8 mm, blunt; lemmas evenly and densely pilose, hairs 2.5–3.5 mm, apical lobes 0.6–1.9 mm, membranous; awns 4–11 mm, readily deciduous, straight to once-geniculate, scabrous; paleas 4–5.6 mm, from as long as to slightly longer than the lemmas; anthers 1.6–2 mm, dehiscent, not penicillate. Caryopses 3.5–4.5 mm, fusiform. 2n = 32.

Achnatherum webberi grows in dry, open flats and on rocky slopes, often with sagebrush, at 1500–2500 m. It grows at scattered locations from Oregon and Idaho to California and Nevada. It differs from A. hymenoides in its cylindrical floret and non-saccate glumes, and from A. pinetorum and A. parishii subsp. parishii in its shorter, deciduous awns. It also has narrower blades than A. parishii subsp. depauperatum.

 

23. Achnatherum swallenii (C.L. Hitchc. & Spellenb.) Barkworth
Swallen’s Needlegrass

Plants tightly cespitose, not rhizomatous. Culms 15–25 cm tall, 0.5–1 mm thick, glabrous; nodes 2–3. Basal sheaths mostly glabrous, pubescent at the base, throats glabrous; collars, including the sides, glabrous; basal ligules 0.2–0.3 mm, obtuse to rounded, glabrous; upper ligules to 0.5 mm, rounded to broadly acute; blades 0.4–0.7 mm wide, arcuate, abaxial surfaces smooth or scabridulous, adaxial surfaces with hairs shorter than 0.5 mm. Panicles 3–6.5 cm long, 0.3–0.7 cm wide; branches appressed, lower branches 1–5 cm, with 1–5 spikelets. Glumes subequal, 4–5.5 mm, not saccate, apices narrowly acute to acuminate, midveins often prolonged into an awnlike tip; lower glumes 0.6–1 mm wide, apices narrowly acute; florets 2.5–3.5 mm long, 0.6–0.8 mm thick, fusiform, terete; calluses 0.1–0.2 mm, blunt; lemmas evenly hairy, hairs 0.3–0.5 mm, all similar in length, apical lobes 0.3–0.5 mm, thickly membranous; awns 5–6 mm, once-geniculate, readily deciduous, basal segment scabridulous; paleas 2.2–2.5 mm, slightly shorter than the lemmas; anthers 1.5–2 mm, dehiscent, not penicillate. Caryopses 2–3 mm, ovoid. 2n = 34.

Achnatherum swallenii grows on open, rocky sites, frequently with low sagebrush, in Idaho and western Wyoming, at 1500–2200 m. It is a dominant species in parts of eastern Idaho, although it is poorly represented in collections.

 

24. Achnatherum wallowaense J.R. Maze & K.A. Robson
Wallowa Needlegrass

Plants tightly cespitose, not rhizomatous. Culms (10)15–40 (45) cm tall, 0.5–0.7 mm thick, glabrous; nodes 1–2. Basal sheaths becoming flat with age, glabrous; collars glabrous, including the sides; basal ligules 0.8–1.3 mm, membranous, truncate to broadly acute, glabrous; upper ligules to 1.6 mm; blades tightly valvate to involute, 0.5–0.8 mm in diameter, abaxial surfaces scabridulous, adaxial surfaces hairy, sometimes densely hairy, hairs shorter than 0.05 mm. Panicles (4)5–13(15) cm long, to 10 cm wide, lax; branches divergent, flexuous, longest branches 2–10 cm, with spikelets confined to the distal portions, drooping. Glumes obtuse to acute; lower glumes 3.5–7 mm long, 0.8–1.3 mm wide, 5(7)-veined; upper glumes 3–6.5 mm, 3-veined; florets 3–5.5 mm long, 1–1.5 mm thick, fusiform, terete; calluses 0.1–0.2 mm, blunt; lemmas coriaceous, shiny, glabrous, black to dark brown at maturity, margins overlapping at maturity, apices thickened dorsally; awns 5–11 mm, readily deciduous, not or weakly geniculate, scabrous; paleas 2.8–4.5 mm, similar to the lemmas in texture, glabrous; anthers 1.6–1.8 mm, dehiscent, not penicillate. Caryopses 2–4 mm, ovoid. 2n = unknown.

Achnatherum wallowaense grows in shallow, rocky soil at scattered localities, from 1000–1600 m, in the Wallowa and Ochoco mountains, Oregon.

 

25. Achnatherum hendersonii (Vasey) Barkworth
Henderson’s Needlegrass

Plants tightly cespitose, not rhizomatous. Culms 10–35 cm tall, 0.3–0.9 mm thick, pub-escent below the nodes, glab-rous or sparsely puberulent elsewhere; nodes 1–2. Basal sheaths completely or mostly glabrous, margins sometimes ciliate distally; collars glabrous; ligules 0.4–1 mm, hyaline, glabrous or pubescent, rounded; blades tightly folded or convolute, to 1 mm wide or thick, abaxial surfaces scabrous, adaxial surfaces pubescent. Panicles 4–12 cm long, 2–5 cm wide, erect; branches and pedicels straight, appressed to strongly ascending, longest branches 2–7 cm. Glumes subequal, 3.5–5.5 mm long, 1–1.5 mm wide, 5-veined; lower glumes obtuse, apices rounded to acute; upper glumes rounded to obtuse, subequal or to 1 mm shorter than the lower glumes; florets 3.5–4.5 mm long, 1–1.5 mm wide, fusiform, laterally compressed; calluses 0.3–0.5 mm, blunt; lemmas coriaceous, glabrous, shiny, apical lobes about 0.2 mm long, thick; awns 6–10 mm, readily deciduous, not geniculate, scabrous; paleas about 3 mm, from 3/4 as long as to equaling the lemmas, indurate, glabrous, apices rounded, flat; anthers about 2.5 mm, dehiscent, penicillate. Caryopses 2.5–4 mm. 2n = 34.

Achnatherum hendersonii grows in dry, rocky, shallow soil, in sagebrush or ponderosa pine associations. It is known from only three counties: Yakima and Kittitas counties, Washington, and Crook County, Oregon. Maze (1981) noted that, at one site, A. hendersonii was restricted to areas subject to frost heaving, although under cultivation, it can grow without such disturbance. He hypothesized that its survival in such sites is attributable to a competitive advantage gained by the structure of its root system. Unlike Poa secunda, which grew in the surrounding, undisturbed areas, the outer cortex and epidermis of the roots of A. hendersonii form a sheath around the stele and inner cortex. When the roots are pulled, this sheath slips and breaks but the internal structures remain intact. In Poa secunda, the outer part of the root is attached to the central core and, when the roots are pulled, they break. Achnatherum hendersonii also differs from P. secunda in having relatively few (9–12), evenly distributed roots that extend to 30 cm.

 

26. Achnatherum hymenoides (Roem. & Schult.) Barkworth
Indian Ricegrass

Plants tightly cespitose, not rhizomatous. Culms 25–70 cm tall, 0.7–1.3 mm thick, glabrous or partly scabridulous; nodes 3–4. Sheaths glabrous or scabridulous, sometimes puber-ulent on the distal margins, hairs to 0.8 mm; collars glabrous, sometimes with tufts of hair on the sides, hairs to 1 mm; basal ligules 1.5–4 mm, hyaline, glabrous, acute; upper ligules to 2 mm; blades usually convolute, 0.1–1 mm in diameter, abaxial surfaces smooth or scabridulous, adaxial surfaces pubescent. Panicles 9–20 cm long, 8–14 cm wide; branches ascending to strongly divergent, longest branches 3–15 cm; pedicels paired, conspicuously divaricate, shorter pedicels in each pair usually at least 1/2 as long as the longer pedicels. Glumes subequal, 5–9 mm long, 0.8–2 mm wide, saccate below, puberulent, hairs about 0.1 mm, tapering above midlength, apices acuminate; lower glumes 5-veined at the base, 3-veined at midlength; upper glumes 5–7-veined at the base; florets 3–4.5 mm long, 1–2 mm thick, obovoid; calluses 0.4–1 mm, sharp; lemmas indurate, densely and evenly pilose, hairs 2.5–6 mm, easily rubbed off, apices not lobed; awns 3–6 mm, rapidly deciduous, not geniculate, scabrous; paleas subequal to the lemmas in length and texture, glabrous, apices pinched; anthers 1.5–2 mm, penicillate, dehiscent, well-filled. Caryopses 2–3 mm. 2n = 46, 48.

Achnatherum hymenoides grows in dry, well-drained soils, primarily in the western part of the Flora region and northern Mexico. Specimens from further east may be introduced; it is unknown whether they have persisted. The roots of A. hymenoides are often surrounded by a rhizosheath formed by mucilaginous secretions to which soil particles attach. This rhizosheath harbors nitrogen-fixing organisms that probably contribute to the success of the species as a colonizer.

Native Americans used the seeds of Achnatherum hymenoides for food. It is also one of the most palatable native grasses for livestock. Several cultivars have been developed for use in restoration work, and it is becoming increasingly available for use as an ornamental.

Achnatherum hymenoides forms natural hybrids with other members of the Stipeae. See discussion on hybrids involving A. hymenoides here.

 

27. Achnatherum arnowiae (S.L. Welsh & N.D Atwood) Barkworth
Arnow’s Ricegrass

Plants tightly cespitose, not rhizomatous. Culms 15–75 cm tall. Sheaths smooth, mostly glabrous, margins ciliate; collars glabrous, with or with-out tufts of hair at the sides, hairs 0.7–2 mm; ligules 1–4 mm, glabrous or sparsely hairy, acute, sometimes ciliate; blades 1–2 mm wide, involute, 0.5–1 mm in diameter, abaxial surfaces scabridulous or smooth, adaxial surfaces densely hairy, hairs about 0.2 mm. Panicles 5–20 cm long, 0.5–2.8 cm wide, loosely contracted; branches strongly ascending, longest branches 0.5–2.5(5) cm. Spikelets evenly distributed along the branches; pedicels loosely appressed to the branches, paired, unequal, shorter pedicels in each pair usually less than 1/2 as long as the longer pedicels. Glumes slightly unequal, saccate below, tapering from about midlength, veins and sometimes also the intercostal regions puberulent, hairs to 0.1 mm, apices acute to acuminate; lower glumes 5.1–6.1 mm; upper glumes 4.3–5.2 mm; florets 2.8–4.2 mm, ovoid; calluses 0.2–0.4 mm, acute; lemmas indurate, dark gray-brown, smooth, densely pilose, hairs at midlength and at the apices similar, 2–3 mm, easily rubbed off, apices not lobed; awns 3–4.4 mm, rapidly deciduous, not geniculate, scabrous; paleas similar to the lemmas in length and texture, glabrous, apices pinched; anthers about 1 mm, dehiscent, penicillate. Caryopses 1–1.7 mm long, 0.8–1 mm in diameter, globose to obovoid. 2n = unknown.

Achnatherum arnowiae grows in pinyon-juniper, sagebrush, and mixed desert shrub communities in Utah, at 1400–2000 m. Welsh and Atwood (2003) state that specimens belonging to A. arnowiae are often filed as A. ×bloomeri, and they suggest that this species may also be hybrid in origin, possibly with Hesperostipa comata as one of its parents. Another possibility is that it is a derivative of A. hymenoides that is adapted to particular soil types.

 

28. Achnatherum contractum (B.L. Johnson) Barkworth
Contracted Ricegrass

Plants tightly cespitose, not rhizomatous. Culms 30–50 cm tall, 1–1.3 mm thick, glabrous; nodes 3–4. Sheaths glabrous; collars puberulent, hairs about 0.2 mm, sometimes the margins with poorly developed tufts of hair to 0.5 mm; ligules 1.8–5 mm, broadly to narrowly acute, glabrous; blades 0.5–1.5 mm wide, flat or convolute, abaxial surfaces smooth, adaxial surfaces scabridulous. Panicles 6–25 cm long, 7–15 cm wide; branches ascending to strongly divergent, longest branches 5–8 cm; pedicels appressed to the branches, paired, unequal, shorter pedicels in each pair usually less than 1/2 as long as the longer pedicels. Spikelets confined to the distal 1/2 of the branches. Glumes saccate below, tapering at midlength, glabrous, midveins sometimes scabridulous, apices acuminate; lower glumes 5.5–7 mm long, 0.9–1.5 mm wide; upper glumes about 0.3 mm shorter; florets 2.5–3.5 mm long, 0.7–1.5 mm thick, fusiform to obovoid; calluses 0.3–0.5 mm, blunt; lemmas densely pilose, hairs at midlength and on the apices similar, 1.2–2 mm, apical lobes 0.5–0.6 mm; awns 6.5–9 mm, readily deciduous, scabrous; paleas similar to the lemmas in length, texture, and pubescence, distal hairs exceeding the paleal apices, apices rounded, flat; anthers about 1.5 mm, penicillate, dehiscent, well-filled. Caryopses 1.5–2.5 mm, globose to obovoid. 2n = 48.

Achnatherum contractum grows in rocky grasslands in eastern Idaho, southwestern Montana, and Wyoming. It is a fertile derivative of a Piptatherum micranthum x Achnatherum hymenoides hybrid (Shechter and Johnson 1968; Shechter 1969). Immature specimens of A. hymenoides are sometimes confused with A. contractum because they have contracted panicles with appressed branches and pedicels; they differ in having pedicel pairs in which the shorter pedicel is more than half as long as the longer pedicel.

 

Achnatherum xbloomeri (Bol.) Barkworth and other hybrids involving A. hymenoides

Numerous natural hybrids exist between Achnatherum hymenoides and other members of the Stipeae. Johnson (1945, 1960, 1962, 1963, 1972) described several of these; all are sterile. Using the treatment adopted here, Johnson’s hybrids have as the second parent A. occidentale (all subspecies), A. thurberianum, A. scribneri, A. robustum, Jarava speciosa, and Nassella viridula. Evidence from herbarium specimens suggests that A. hymenoides also forms sterile hybrids with other species of Achnatherum. The name Achnatherum xbloomeri applies only to hybrids between A. hymenoides and A. occidentale subsp. occidentale, but plants keying here may include any of the other interspecific hybrids. They all differ from A. hymenoides in having more elongated florets and awns 10–20 mm long, and from their other parent, in most instances, in having longer lemma hairs and more saccate glumes. Identification of the second parent is best made in the field by noting which other species of Stipeae are present, bearing in mind that species that are not in anthesis at the same time in one year might have sufficient overlap for hybridization in other years.

Of the two intergeneric hybrids mentioned above, that with Nassella viridula is treated as ×Achnella caduca. It differs from Achnatherum hymenoides in its longer glumes and florets, and from other A. hymenoides hybrids in having a readily deciduous awn. No binomial has been proposed for the hybrid with Jarava speciosa. There is one fertile intergeneric hybrid involving A. hymenoides, A. contractum. It is included in Achnatherum and described below because it resembles other members of Achnatherum more than it does Piptatherum, the genus of the other parent.

Sterile hybrids have anthers that do not dehisce, and contain few, poorly formed pollen grains. They also fail to form good caryopses, but this is also true of some non-hybrid plants. In the case of non-hybrid plants, failure to form good caryopses can result from failure to capture pollen or from incompatibility between the pollen grain and the pistillate plant. It is not known which, if either, of these explanations accounts for the large number of empty caryopses found in Achnatherum hymenoides.