10.04 PIPTATHERUM P. Beauv.
Mary E. Barkworth

Plants perennial; cespitose or soboliferous, sometimes rhizomatous. Culms 10–140(150) cm, erect, usually glabrous, usually smooth; nodes 1–6; branching intra- or extravaginal at the base, not branching above the base; prophylls concealed by the leaf sheaths. Leaves sometimes basally concentrated; cleistogenes not present; sheaths open, glabrous, smooth to scabrous; auricles absent; ligules 0.2–15 mm, membranous to hyaline; blades 0.5–16 mm wide, flat, involute, valvate, or folded, often tapering in the distal 1/3, apices acute to acuminate, not stiff, basal blades not overwintering, sometimes not developed, flag leaf blades well developed, longer than 1 cm. Inflorescences 3–40 cm, terminal panicles, open or contracted; branches straight or flexuous, usually scabrous, rarely smooth; pedicels often appressed to the branches. Spikelets 1.5–7.5 mm, with 1 floret; rachillas not prolonged beyond the floret; disarticulation above the glumes, beneath the floret. Glumes from 1 mm shorter than to exceeding the florets, subequal or the lower glumes longer than the upper glumes, membranous, 1–9-veined, veins evident, apices obtuse to acute or acuminate; florets 1.5–10 mm, usually dorsally compressed, sometimes terete; calluses 0.1–0.6 mm, glabrous or with hairs, blunt; lemmas 1.2–9 mm, smooth, coriaceous or stiffly membranous, tawny or light brown to black at maturity, 3–7-veined, margins flat, separated and parallel for their whole length at maturity, apices not lobed or lobed, glabrous or hairy, hairs about 0.5 mm, not spreading, awned, lemma-awn junction evident; awns 1–18(20) mm, centric, often caducous, almost straight to once- or twice-geniculate, scabrous; paleas as long as or slightly longer than the lemmas, similar in texture and pubescence, 2(3)-veined, not keeled over the veins, flat between the veins, veins terminating near the apices, apices often pinched; anthers 3, 0.6–5 mm, sometimes penicillate; styles 2 and free to their bases, or 1 with 2–3 branches. Caryopses glabrous, ovoid to obovoid; hila 1/2 as long as to equaling the length of the caryopses. x = 11, 12. Name from the Greek pipto, ‘fall’, and ather, ‘awn’.

Piptatherum has approximately 30 species, most of which are Eurasian. They extend from lowland to alpine regions, and grow in habitats ranging from mesic forests to semideserts.

The pistils in Piptatherum exhibit variability in the development of the styles, a feature that can be seen only in florets shortly before or at anthesis. This variability is reported in the descriptions, but the number of specimens examined per species is low, sometimes only one.

SELECTED REFERENCES Curto, M.L. and D.H. Henderson. 1998. A new Stipa (Poaceae: Stipeae) from Idaho and Nevada. Madroño 45:57–63; Freitag, H. 1975. The genus Piptatherum (Gramineae) in southwest Asia. Notes Roy. Bot. Gard. Edinburgh 42:355–489; 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. Cytotaxonomic studies in Oryzopsis. Bot. Gaz. 107:1–32.

 

For an interactive dichotomous key, click here; the interactive, multientry key is not yet available.

 

1. Basal leaf blades 0–2 cm long; cauline leaf blades 8–16 mm wide; florets 4.5–7.5 mm long ... P. racemosum
1. Basal leaf blades 4–45 cm long; cauline leaf blades 0.5–10 mm wide; florets 1.5–6 mm long ... 2
2. Lemmas and calluses usually glabrous, occasionally sparsely pubescent; florets 1.5–2.5 mm long ... 3
3. Blades 0.5–2.5 mm wide, often involute; panicles 5–20 cm long, the lower nodes with 1–3 branches ... P. micranthum (in part)
3. Blades 2–10 mm wide, flat; panicles 10–40 cm long, the lower nodes usually with 3–7 branches, sometimes with 15–30+ branches ... P. miliaceum
2. Lemmas evenly pubescent; calluses hairy; florets 1.5–6 mm long ... 4
4. Awns 3.9–15 mm long, persistent, once- or twice-geniculate ... 5
5. Primary panicle branches straight, appressed; awns 3.9–7 mm long; florets 3–6 mm long ... P. exiguum
5. Primary panicle branches somewhat flexuous, often divergent; awns 5–15 mm long; florets 2.2–4.5 mm long ... P. canadense
4. Awns 1–8 mm long, caducous, often absent from herbarium specimens, straight or arcuate ... 6
6. Awns 4–8 mm long; florets 1.5–2.5 mm long ... P. micranthum (in part)
6. Awns 1–2.5 mm long; florets 2.2–4.5 mm long ... 7
7. Lower panicle branches straight; ligules 0.5–2.5 mm long ... P. pungens
7. Lower panicle branches flexuous; ligules 1.8–5.5 mm long ... P. shoshoneanum

 

1. Piptatherum exiguum (Thurb.) Dorn
Little Piptatherum

Plants tightly cespitose, not rhizomatous. Culms 12–40 cm, sometimes not exceeding the basal leaves, scabridulous; basal branching mostly intravaginal. Leaves basally concentrated; sheaths mostly smooth, some-times scabridulous distally; ligules 1.2–3.5 mm, acute; basal blades 9–30 cm long, 0.6–1.4 mm wide when open, usually valvate and 0.4–0.8 mm in diameter, both surfaces scabrous. Panicles 3.5–9 cm, lower nodes with 1–2 branches; branches straight, tightly appressed to the rachises, lower branches 1–2 cm, with 1–2 spikelets. Glumes subequal, 3.5–6 mm long, 1.8–2.2 mm wide, ovate, apices acute; florets 3–6 mm, terete; calluses 0.2–0.5 mm, hirsute, disarticulation scars circular; lemmas evenly pubescent, tan or gray-brown at maturity, margins not overlapping at maturity, apical lobes 2, 0.3–0.4 mm, thick; awns 3.9–7 mm, persistent, strongly once-geniculate, basal segment twisted; paleas not exceeding the lemma lobes, similar in texture and pubescence; anthers 1.5–3 mm; ovaries with a conelike extension bearing a 3-branched style. Caryopses about 2.5 mm long, 1 mm thick; hila linear, 9/10 as long as to equaling the caryopses. 2n = 22.

Piptatherum exiguum grows on rocky slopes and outcrops in upper montane habitats, from central British Columbia to southwestern Alberta and south to northern California, Nevada, Utah, and northern Colorado. The limited DNA evidence available suggests that it is a basal species within Piptatherum (Jacobs et al. 2006).

 

2. Piptatherum canadense (Poir.) Dorn
Canadian Piptatherum, Oryzopsis du Canada

Plants cespitose, not rhizom-atous. Culms 30–90 cm, glabrous; basal branching mostly intravaginal. Leaves basally concentrated; sheaths smooth or scabridulous; ligules 1–4 mm, hyaline, truncate, rounded, or acute; basal blades 4–15 cm long, 1–1.5 mm wide when flat, 0.5–0.8 mm in diameter when folded or convolute. Panicles 9–15 cm, lower nodes with 1–2 branches; branches 1–6 cm, somewhat flexuous, ascending to divergent. Glumes subequal, 3–6 mm long, 1.3–2 mm wide, ovate, 1–3-veined, apices acute to mucronate; florets 2.2–4.5 mm, obovoid, dorsally compressed; calluses 0.2–0.5 mm, hairy, disarticulation scars elliptic; lemmas coriaceous, evenly pubescent, tan at maturity, margins widely separated even when immature; awns 5–15 mm, persistent, once- or twice-geniculate, first segments strongly twisted; paleas similar to the lemmas in length, texture, and pubescence; anthers 1–2 mm; ovaries developing 2 conelike style bases, each bearing a single, unbranched style. Caryopses about 2.5 mm long, 0.5 mm thick; hila linear, almost equaling the caryopses. 2n = 22.

Piptatherum canadense grows in grasslands and open woods, from the British Columbia–Alberta border east to Newfoundland, extending south into the Great Lakes region and the northeastern United States. Its persistent, longer awns distinguish P. canadense from P. pungens.

 

3. Piptatherum pungens (Torr.) Dorn
Sharp Piptatherum

Plants cespitose, not rhizom-atous. Culms 10–90 cm, usually glabrous, occasionally puber-ulent beneath the nodes; basal branching intravaginal. Leaves basally concentrated; sheaths smooth or somewhat scabrous; ligules 0.5–2.5 mm, truncate to acute; blades (6)18–45 cm long, 0.5–1.8 mm wide, flat to convolute, abaxial surfaces scabridulous to scabrous, adaxial surfaces scabrous. Panicles 4–6 cm, lower nodes with 1–2 primary branches; branches 0.8–4 cm, straight, usually strongly ascending, ascending to divergent at anthesis. Glumes subequal, 3.5–4.5 mm long, 1.4–2 mm wide, from 1 mm shorter than to slightly exceeding the florets, ovate, usually 1-veined, sometimes 3–5-veined near the base, apices rounded or acute; florets 3–4 mm, dorsally compressed; calluses 0.2–0.3 mm, rounded, hairy, disarticulation scars circular; lemmas evenly pubescent, margins not overlapping at maturity; awns 1–2 mm, straight, slightly twisted, caducous, often absent even from immature florets; paleas equaling or almost equaling the lemma lobes, similar in texture and pubescence to the lemmas; anthers 0.8–1.8 mm, usually not penicillate; ovaries with a conelike extension bearing a 2-branched style. Caryopses about 1.8 mm long, about 0.9 mm wide; hila linear, 9/10 as long as to equaling the caryopses. 2n = 22, 24.

Piptatherum pungens grows in sandy to rocky soils and open habitats, from southern Yukon Territory across Canada to the Great Lakes region and eastern Pennsylvania, and, as a disjunct, in the western Great Plains and the southern Rocky Mountains. Its apparent absence from Idaho and Montana, and almost complete absence from Wyoming, is puzzling. The awns of P. pungens fall off so rapidly that it is sometimes mistaken for Milium or Agrostis, but the only perennial species of Milium in the Flora region has leaf blades 8–17 mm wide, and no species of Agrostis has such stiff lemmas and well-developed paleas. Its deciduous, shorter awns distinguish it from P. canadense.

 

4. Piptatherum micranthum (Trin. & Rupr.) Barkworth
Small-Flowered Piptatherum

Plants loosely cespitose, not rhizomatous. Culms 20–85 cm, glabrous; basal branching extravaginal. Leaves basally concentrated; sheaths glabrous; ligules 0.4–1.5(2.5) mm, truncate; blades 5–16 cm long, 0.5–2.5 mm wide, usually involute. Panicles 5–20 cm, lower nodes with 1–3 branches; branches 2–6 cm, divergent to reflexed at maturity, with 3–10(15) spikelets, secondary branches appressed to the primary branches. Glumes 2.5–3.5 mm, acute; lower glumes 1(3)-veined; upper glumes 3-veined; florets 1.5–2.5 mm, dorsally compressed; calluses 0.1–0.2 mm, glabrous or sparsely hairy, disarticulation scars circular; lemmas usually glabrous, sometimes sparsely pubescent, brownish, shiny, 5-veined, margins not overlapping at maturity; awns 4–8 mm, straight or almost so, caducous; anthers 0.6–1.2 mm, not penicillate; ovaries truncate to rounded, bearing 2 separate styles. Caryopses about 1.2 mm long, about 0.8 mm wide; hila linear, 3/4–9/10 as long as the caryopses. 2n = 22.

Piptatherum micranthum grows on gravel benches, rocky slopes, and creek banks, from British Columbia to Manitoba and south to Arizona, New Mexico, and western Texas. The combination of small, dorsally compressed florets and appressed pedicels distinguishes this species from all other native North American Stipeae.

Achnatherum contractum is the fertile derivative of hybridization between Piptatherum micranthum and A. hymenoides. It is placed in Achnatherum because it resembles that genus more than Piptatherum.

 

5. Piptatherum shoshoneanum (Curto & Douglass M. Hend.) P.M. Peterson & Soreng
Shoshone Piptatherum

Plants tightly cespitose, not rhizomatous. Culms 20–50 cm, internodes smooth to scabrid-ulous; nodes glabrate; basal branching intravaginal. Leaves basally concentrated; ligules 1.8–5.5 mm, hyaline, acute, often lacerate; blades 4–16 cm long, 1–2.5 mm wide when flat, 0.6–1 mm in diameter when involute, abaxial surfaces smooth or scabridulous, adaxial surfaces scabridulous. Panicles 3.3–22 cm, lower nodes with 1–2(4) branches; branches 1.8–11.6 cm, flexuous, initially appressed, becoming strongly divergent to reflexed, secondary and tertiary branches appressed to the primary branches. Glumes subequal, 3.2–5.3 mm, exceeding the florets by 0.2–1.5 mm, ovate to broadly lanceolate, 1–9-veined, apices acute to acuminate; florets 2.4–4.1 mm, dorsally compressed; calluses about 0.3 mm, hairy, disarticulation scars round; lemmas coriaceous, evenly pubescent, hairs to 0.5 mm, becoming tawny with age, margins not overlapping at maturity; awns 1–2.5 mm, straight or slightly arcuate, caducous; paleas 2.1–3.6 mm, similar to the lemmas in texture and pubescence; anthers 1.7–2.2 mm, penicillate; ovaries truncate, bearing 2 styles. Caryopses 1.8–2 mm long, about 0.8 mm thick; hila linear, about 9/10 the length of the caryopses. 2n = 20.

Piptatherum shoshoneanum is known best from eastern Idaho, where it grows in the canyons of the Middle Fork of the Salmon River and its tributaries. It has also been found 750 km to the southwest in the Belted Range of southwestern Nevada. So far, fieldwork on the intervening mountain ranges has not revealed additional populations. It usually grows in moist crevices of igneous, metamorphic, or sedimentary cliffs and rock walls.

 

6. Piptatherum racemosum (Sm.) Eaton
Mountain Ricegrass

Plants loosely cespitose to soboliferous, rhizomatous. Culms 48–80 cm, scabrous or pubescent adjacent to the nodes; basal branching extravaginal. Leaves not basally concen-trated; sheaths usually smooth and glabrous, occa-sionally scabridulous and inconspic-uously pubescent near the margins; ligules of upper leaves 0.3–0.7 mm, truncate; blades of basal leaves 0–2 cm; blades of upper leaves 10–27 cm long, 8–16 mm wide, abaxial surfaces evenly but sparsely pubescent, adaxial surfaces with straight hairs to 0.3 mm on the primary veins and flexuous hairs of 0.5–0.9 mm on the minor veins, tapering from near midlength to the apices. Panicles 12–25 cm, lower nodes with 1–2 branches; branches 3–9.5 cm, straight, strongly ascending to strongly divergent, with 2–5 spikelets. Glumes 6–8 mm, from subequal to the florets to exceeding the florets by 2 mm, ovate, 5–7-veined, acuminate; florets 4.5–7.5 mm; calluses 0.3–0.6 mm, disarticulation scars circular; lemmas coriaceous, sparsely pubescent to glabrate throughout, margins fused at the base, not overlapping, shiny dark brown to black at maturity; awns 10–25 mm, deciduous, slightly twisted, flexuous; anthers 3.5–5.5 mm, not penicillate; ovaries developing 2 conelike extensions, each terminating in a style. Caryopses 5–6 mm; hila linear, 4/5–9/10 as long as the caryopses. 2n = 46, 48.

Piptatherum racemosum usually grows in deciduous woods, and less often in open pine woods, in rocky, mountainous areas, from the St. Lawrence and Ottawa rivers south to the Missouri River, Tennessee, and Virginia, and east to Maine. The absence of basal blades and the dark, shiny lemmas distinguish it from all other North American Stipeae. It is highly palatable to livestock, but is never sufficiently abundant to be important as forage.

 

7. Piptatherum miliaceum (L.) Coss.
Smilo Grass

Plants loosely cespitose, not rhizomatous. Culms 40–150 cm, glabrous, often branching at the lower cauline nodes; basal branching extravaginal. Leaves not basally concen-trated; sheaths glabrous, persis-tent; ligules of lower leaves 0.5–1.5 mm, truncate; ligules of upper leaves 1.5–4 mm, rounded to sharply acute; blades 5–30 cm long, 2–10 mm wide, flat, smooth on both surfaces. Panicles 10–40 cm, lax, lower nodes either with 3–7 branches bearing 10–40 functional spikelets, or with 15–30+ branches with no functional spikelets; primary branches spreading to ascending; lower branches 3–8 cm; secondary branches diverging from the primary branches. Glumes 2.5–3.5 mm, acuminate, 3-veined; florets 1.5–2 mm, dorsally compressed; calluses about 0.3 mm, glabrous, dis-articulation scars circular; lemmas stiffly membranous, glabrous, margins fused at the base, not overlapping, light brown at maturity; awns 3–4 mm; anthers 2–2.5 mm, penicillate; ovaries rounded, bearing two styles. Caryopses 1.5–1.7 mm long, about 0.8 mm thick; hila linear, about 1/2 as long as the caryopses. 2n = 24.

Piptatherum miliaceum is a Eurasian introduction that is now established in several parts of the world. In its native range it grows, often as a common species, primarily in disturbed areas, wadis, and oases, penetrating into the semidesert regions of northern Africa and western Asia. It is used as a fodder plant in northern Africa. Within the Flora region, P. miliaceum is known from Arizona and California, growing in disturbed sites. It has also been found on a ballast dump in Maryland.

1. Panicle branches loosely whorled, lower nodes with 3–7 branches, all spikelet-bearing ... subsp. miliaceum
1. Panicle branches densely whorled, lower nodes with 15–30+ branches, some with highly reduced or no spikelets ... subsp. thomasii

 

Piptatherum miliaceum (L.) Coss. subsp. miliaceum

Branches loosely whorled; lower nodes with 3–7 spikelet-bearing branches.

Piptatherum mileaceum subsp. miliaceum is the most common of the two subspecies, and the only one known to be established in the Flora region.

 

Piptatherum miliaceum subsp. thomasii (Duby) Soják

Branches densely whorled; lower nodes with 15–30+ branches, some sterile, bearing highly reduced or no spikelets.

Piptatherum miliaceum subsp. thomasii has a native range similar to that of subsp. miliaceum, except that it does not grow in semidesert regions. In the Flora region, it is known only from cultivated specimens.