20.02   DANTHONIA DC.
Stephen J. Darbyshire

Plants perennial; cespitose, sometimes shortly rhizomatous. Culms 7-130 cm, erect. Sheaths open to the base, with tufts of hairs at the auricle position, sometimes with a line of hairs around the collar; auricles absent; ligules of hairs; blades rolled in the bud, flat or involute when dry. Inflorescences terminal; panicles, racemes, or a solitary spikelet, to 12 cm; rachises, branches, and pedicels scabrous or hirsute. Spikelets terete or laterally compressed, with 3-12 florets, terminal floret reduced; disarticulation beneath the florets, also at the cauline nodes in some species. Glumes subequal or the lower glumes a little longer than the upper glumes, usually exceeding the florets (excluding the awns and lemma teeth), lanceolate, chartaceous, 1-7-veined, keels glabrous or sparsely scabrous; rachillas glabrous; calluses densely strigose on the sides; lemma bodies obscurely (5)7-11-veined, backs glabrous or pilose, margins usually densely pilose proximally, apices with 2 acute to aristate lobes, mucronate or awned between the lobes; awns, when present, geniculate and twisted below the geniculation; paleas about as long as the lemma bodies, 2-veined, veins scabrous, apices obtuse, sometimes bifid; lodicules 2, glabrous or with a few hairs; anthers 3, their size depending on whether the florets are chasmogamous or cleistogamous; ovaries glabrous. Caryopses 1.5-5.5 mm, ovate to obovate, dorsally flattened, brown; hila linear, 1/3-3/4 as long as the caryopses. Cleistogenes usually present in the lower sheaths, with 1(-10) florets, not disarticulating; rachilla internodes about as long as or longer than the adjacent florets; lemmas coriaceous, glabrous or scabrous near the apex, entire, unawned; paleas sometimes slightly longer than the lemmas; anthers 3, minute; ovaries glabrous; caryopses more linear than in the aerial florets. x = 12. Named for the French botanist Étienne Danthoine, who worked in the early nineteenth century.

Danthonia is interpreted here as a genus of about 20 species that are native in Europe, North Africa, and the Americas. Of the eight species found in the Flora region, seven are native and one is an introduction that is now established.


SELECTED REFERENCES Baeza P., C.M. 1996. Los géneros Danthonia DC. y Rytidosperma Steud. (Poaceae) en América-Una revisión. Sendtnera 3:11-93; Darbyshire, S.J. and J. Cayouette. 1989. The biology of Canadian weeds. 92. Danthonia spicata (L.) Beauv. in Roem. & Schult. Canad. J. Pl. Sci. 69:1217-1233; Dobrenz, A.K. and A.A. Beetle. 1966. Cleistogenes in Danthonia. J. Range Managem. 19:292-296; Dore, W.G. 1971. Sieglingia decumbens (L.) Bernh.-Pulvini of palea. Watsonia 8:297-299; Dore, W.G. and J. McNeill. 1980. Grasses of Ontario. Research Branch, Agriculture Canada Monograph No. 26. Canadian Government Publishing Centre, Hull, Québec, Canada. 566 pp.; Linder, H.P. and G.A. Verboom. 1996. Generic limits in the Rytidosperma (Danthonieae, Poaceae) complex. Telopea 6:597-627; Quinn, J.A.. 1975. Variability among Danthonia sericea (Gramineae) populations in responses to substrate moisture levels. Amer. J. Bot. 62:884-891; Quinn, J.A. and D.E. Fairbrothers. 1971. Habitat ecology and chromosome numbers of natural populations of the Danthonia sericea complex. Amer. Midl. Naturalist 85:531-536; Quinn, J.A., J. Rotsettis, and D.E. Fairbrothers. 1972. Inflorescence characters and reproductive proficiency in Danthonia sericea populations. Amer. J. Bot. 59:942-951; Rotsettis, J., J.A. Quinn, and D.E. Fairbrothers. 1972. Growth and flowering of Danthonia sericea populations. Ecology 53:227-234; Tzvelev, N.N.1976. Zlaki SSSR. Nauka, Leningrad [St. Petersburg], Russia. 788 pp. [In Russian].

NOTE: In the key and descriptions, lemma lengths do not include the apical teeth. Callus characteristics are best seen on the middle to upper florets in the spikelet.

1
Lemmas mucronate, not awned ..... 1. D. decumbens
Lemmas not mucronate, with a twisted, geniculate awn (2)
2
Calluses of the middle florets from shorter to slightly longer than wide, convex abaxially; lemma bodies 2.5-6 mm long, the backs usually pilose, occasionally glabrous or sparsely pilose (3)
Calluses of the middle florets longer than wide, concave abaxially; lemma bodies 3-11 mm long, the backs usually glabrous or sparsely pilose (pilose in D. parryi) (5)
3
Awns 10-17 mm; hairs of the lemma margins evidently increasing in length distally, longest hairs 2.5-4 mm long ..... 2. D. sericea
Awns 5-10 mm; hairs of the lemma margins not evidently increasing in length distally, longest hairs 0.5-2 mm long (4)
4
Lemma lobes 2-4 mm long, usually 2/3 or more as long as the lemma bodies, aristate; lower inflorescence branches usually flexible, divergent after anthesis; pedicels on the lowest inflorescence branch as long as or longer than the spikelets; leaves not curling at maturity ..... 3. D. compressa
Lemma lobes 0.5-2 mm long, less than 2/3 as long as the lemma bodies, acute to aristate; inflorescence branches stiff, appressed to strongly ascending after anthesis; pedicels on the lowest inflorescence branch from shorter than to equaling the spikelets; blades usually becoming curled at maturity ..... 4. D. spicata
5
Lower inflorescence branches (pedicels if the inflorescence racemose) stiff, erect; pedicels from shorter than to as long as the spikelets (6)
Lower inflorescence branches (pedicels if the inflorescence racemose) flexible, slightly to strongly divergent; pedicels usually as long as or longer than the spikelets (sometimes shorter in D. parryi) (7)
6
Spikelets 1(-3), if 2-3, the inflorescence a raceme; lemma bodies 5.5-11 mm; mature culms disarticulating at the nodes ..... 8. D. unispicata
Spikelets (4)5-10; lower inflorescence branches usually with 2-3 spikelets; lemma bodies 3-6 mm; mature culms not disarticulating at the nodes ..... 5. D. intermedia
7
Uppermost cauline blades usually strongly divergent or reflexed; inflorescences usually racemose; pedicels usually much longer than the spikelets and usually strongly divergent; lemmas glabrous or sparsely hairy over the back; mature culms disarticulating at the nodes ..... 7. D. californica
Uppermost cauline blades usually erect to ascending; inflorescences usually paniculate; pedicels shorter than to as long as the spikelets; lemmas pilose over the back, at least basally; mature culms not disarticulating at the nodes ..... 6. D. parryi


1.   Danthonia decumbens (L.) DC.
Mountain Heath-Grass, Danthonie Décombante

Culms 8-60 cm, usually erect, sometimes decumbent, not disarticulating. Sheaths glabrous or pilose; blades 5-15 cm long, 0.5-4 mm wide, usually flat, glabrous or sparsely pilose. Inflorescences with up to 15 spikelets; branches erect; lower branches with 1-3 spikelets. Spikelets 6-15 mm; florets usually cleistogamous, rarely chasmogamous. Calluses of middle florets from as long as to a little longer than wide, convex abaxially; lemma bodies 5-6 mm, margins glabrous or pubescent for most of their length, scabrous apically, apices with acute teeth, teeth often scabrous, sometimes scabridulous, mucronate, not awned, from between the teeth; palea veins swollen at the base, forming pulvini; anthers of the cleistogamous florets 0.2-0.4 mm, those of the chasmogamous florets about 2 mm. Caryopses 2.1-2.5 mm long, 1.1-1.8 mm wide. 2n = 24, 36, 124.

Danthonia decumbens grows throughout most of Europe, the Caucasus, and northern Turkey, and is now established on the west and east coasts of North America. It grows in heath lands, sandy or rocky meadows, clearings, and sometimes along roadsides. The species is sometimes placed in the monotypic genus Sieglingia, as Sieglingia decumbens (L.) Bernh.


2.   Danthonia sericea Nutt.
Downy Oatgrass

Culms 50-120 cm, not disarticulating. Sheaths usually villous, occasionally glabrous; blades 10-30 cm long, 2-4 mm wide, pilose or glabrous, usually at least the adaxial surface pilose, uppermost cauline blades erect to ascending. Inflorescences with (5)10-25(30) spikelets; lower branches erect to ascending, with 2-6 spikelets; pedicels on the lowest branch from shorter than to subequal to the spikelets. Spikelets 10-20 mm. Calluses of middle florets from as long as to a little longer than wide, convex abaxially; lemma bodies 4-6 mm, usually pilose over the back (sometimes glabrous), margins densely pilose to beyond midlength, hairs evidently increasing in length distally, longest hairs 2.5-4 mm, longer than apical teeth 2-4.5(5.5) mm, aristate; awns 10-17 mm; anthers to 2.6 mm. Caryopses 1.7-2.4 mm long, 0.8-1.2 mm wide. 2n = 36.

Danthonia sericea is restricted to the eastern United States. It grows mostly on sand barrens and in open woods on dry soils. A less common form, with glabrous foliage and lemma backs, is found in bogs, seepage areas, and low moist areas adjacent to lakes and rivers and has been called D. sericea var. epilis (Scribn.) Gleason or D. epilis Scribn. [For comments from Quinn, click here]. Similar patterns of infraspecific variation are also seen in the leaf and lemma vestiture of D. spicata and D. californica, but the genetic basis of this variation is probably not taxonomically significant.


3.   Danthonia compressa Austin
Flattened Oatgrass, Danthonie Comprimée

Culms 40-80 cm, disarticulating at the nodes when mature. Sheaths glabrous, rarely sparsely pilose, usually reddish above the nodes; blades to 30 cm long, 2-4 mm wide, flexible but not curled at maturity, glabrous, sometimes scabrous, uppermost cauline blades erect to ascending. Inflorescences with (4)6-17 spikelets; branches usually flexible, usually divergent, sometimes strongly so, after anthesis; lower branches with 2-3 spikelets; pedicels on the lowest branch as long as or longer than the spikelets. Spikelets (7)10-16 mm. Calluses of middle florets about as long as wide, convex abaxially; lemma bodies 2.5-5 mm, pilose over the back, sometimes sparsely so, margins pilose to beyond midlength, distal hairs 0.5-2 mm, apical teeth 2-4 mm, aristate, (1/2)2/3 or more as long as the lemma bodies; awns 6-10 mm; anthers to 2.2 mm. Caryopses 1.7-2.6 mm long, 0.7-1.1 mm wide. 2n = 36.

Danthonia compressa grows in open and semi-shaded areas, including meadows, open woods, and woodland openings. Although not a true pioneer species, it may sometimes occur as a weed in perennial crops. It is restricted to eastern North America.


4.   Danthonia spicata (L.) P. Beauv. ex Roem. & Schult.
Poverty Oatgrass, Danthonie à Épi

Culms (7)10-70(100) cm, disarticulating at the nodes when mature. Sheaths pilose or glabrous; blades 6-15(20) cm long, 0.8-3(4) mm wide, usually becoming curled at maturity, glabrous or pilose, uppermost cauline blades erect to ascending. Inflorescences with 5-10(18) spikelets; branches stiff, appressed to strongly ascending after anthesis; lower branches with 1-3 spikelets; pedicels on the lowest branch from shorter than to equaling the spikelets. Spikelets 7-15 mm. Calluses of middle florets about as long as wide, convex abaxially; lemma bodies 2.5-5 mm, usually pilose (sometimes glabrous) over the back, margins pilose to about midlength, longest hairs 0.5-2 mm, apical teeth 0.5-2 mm, acute to aristate, less than 2/3 as long as the lemma bodies; awns 5-8 mm; anthers to 2.5 mm. Caryopses 1.5-2(2.3) mm long, 0.7-1 mm wide. 2n = 31, 36.

Danthonia spicata grows in dry rocky, sandy, or mineral soils, generally in open sunny places. Its range includes most of boreal and temperate North America and extends south into northeastern Mexico.

Phenotypically, Danthonia spicata is quite variable, expressing different growth forms under different conditions (Dore and McNeill 1980; Darbyshire and Cayouette 1989). Slow clonal growth, extensive cleistogamy, and limited dispersal contribute to the establishment of morphologically uniform populations, some of which have been given scientific names. For instance, D. spicata var. pinetorum Piper is sometimes applied to depauperate plants and D allenii Austin misapplied to more robust or second growth plants (Dore and McNeill 1980).

Plants of shady or moist habitats often lack the distinctive curled or twisted blades usually found on plants growing in open habits. Such plants, which tend to have smaller spikelets and pilose foliage, have been called D. spicata var. longipila Scribn. & Merr. The terminal inflorescence is usually primarily cleistogamous, but plants with chasmogamous inflorescences are found throughout the range of the species. Chasmogamous plants differ in having divergent inflorescence branches at anthesis, larger anthers, and well-developed lodicules.


5.   Danthonia intermedia Vasey
Timber Oatgrass, Danthonie Intermédiaire

Culms 10-50(70) cm, not disarticulating at maturity. Sheaths usually glabrous; blades 5-10 cm long, 1-3.5 mm wide, glabrous or slightly pilose. Inflorescences with (4)5-10 spikelets; branches stiff, appressed or strongly ascending; lower branches with (1)2-3(5) spikelets; pedicels on the lowest branch shorter than the spikelets. Spikelets 11-15(19) mm. Calluses of middle florets longer than wide, concave abaxially; lemma bodies 3-6 mm, glabrous over the back, densely pilose along the margins, teeth 1.5-2.5 mm, acute to acuminate or aristate; awns 6.5-8 mm; anthers usually tiny, sometimes to 4 mm. Caryopses (2)2.3-3 mm long, 0.7-1.1 mm wide. Cleistogenes rarely produced. 2n = 36, 98.

Danthonia intermedia grows in boreal and alpine meadows, open woods, and on rocky slopes and northern plains. Its range extends from Kamchatka, Russia, to North America, south along the cordillera, and east, through boreal and alpine regions, to Quebec and Newfoundland and Labrador. Its primarily cleistogamous reproduction has probably facilitated its establishment and spread through more boreal and alpine habitats than other members of the genus.

Tzvelev (1976) treats the American plants as Danthonia intermedia Vasey subsp. intermedia and the Russian plants, which have 2n = 18, as Danthonia intermedia subsp. riabuschinskii (Kom.) Tzvelev.


6.   Danthonia parryi Scribn.
Parry's Oatgrass

Culms 30-80(100) cm, not disarticulating at maturity. Sheaths glabrous or sparsely pubescent; blades 15-25 cm long, to 4 mm wide, glabrous or scabrous (rarely pilose), uppermost cauline blades erect or diverging less than 20° from the culm at maturity. Inflorescences usually paniculate, sometimes racemose, with (3)4-11 spikelets; branches appressed to ascending, somewhat flexible; pedicels on the lowest branch from shorter than to as long as the spikelets. Spikelets 16-24 mm. Calluses of middle florets longer than wide, concave abaxially; lemma bodies 5.5-10 mm, backs usually pilose, especially near the base (rarely glabrous), margins pilose, teeth 2.5-8 mm, aristate; awns 12-15 mm; anthers to 6.5 mm. Caryopses rarely produced, 3.5-5.2 mm long, 0.9-1.8 mm wide. 2n = 36.

Danthonia parryi is endemic to western North America and is often a major component of grasslands on the eastern foothills of the Rocky Mountains. It grows in open grassland, open woods, and rocky slopes, at elevations up to 4000 m. It rarely produces caryopses in the terminal inflorescences. This and its somewhat intermediate morphology have led to speculation that it is derived from hybridization between D. californica and D. intermedia.


7.   Danthonia californica Bol.
California Oatgrass

Culms (10)30-130 cm, disarticulating at the nodes at maturity. Sheaths glabrous or pilose, upper sheaths usually glabrous or unevenly pilose; blades 10-30 cm long, (1)2-5(6) mm wide, flat to rolled or involute, glabrous or pilose, uppermost cauline blades strongly divergent to reflexed at maturity. Inflorescences usually racemose, with (2)3-6(10) widely-spreading spikelets; branches flexible, strongly divergent to reflexed at maturity, pulvini usually present at the base; pedicels on the lowest branch longer than the spikelets, often crinkled. Spikelets (10)14-26(30) mm. Calluses of middle florets usually longer than wide, concave abaxially; lemma bodies 5-10 mm, glabrous or sparsely pilose over the back, margins pubescent (rarely glabrous), apical teeth (2)4-6(7) mm, aristate; awns (7)8-12 mm; anthers to 4 mm. Caryopses 2.5-4.2 mm long, 1.3-1.6 mm wide. 2n = 36.

Danthonia californica grows in prairies, meadows, and open woods. It has a disjunct distribution, one portion of its range being located in western North America, the other in Chile. An introduced population has been found at Mansfield, Massachusetts.

Plants with pilose foliage have been called D. californica var. americana (Scribn.) Hitchc. and plants with sparsely pilose lemma backs D. californica var. macounii Hitchc., but the variation does not appear to be taxonomically significant.


8.   Danthonia unispicata (Thurb.) Munro ex Vasey
One-Spike Oatgrass

Culms (10)15-30(42) cm, disarticulating at the nodes at maturity. Sheaths usually densely pilose, hairs sometimes papillose-based (upper sheaths sometimes glabrous); blades 3-8(20) cm long, 1-3 mm wide, both surfaces sparsely to densely pilose, sometimes also scabrous or hirsute (rarely glabrous). Inflorescences with 1-2(3) spikelets, if more than 1, racemose; pedicels stiff, appressed, shorter than the spikelets. Spikelets (8)12-26 mm. Calluses of middle florets longer than wide, concave abaxially; lemma bodies 5.5-11 mm, glabrous over the back (rarely with a few scattered hairs), margins pilose (rarely glabrous), apical teeth 1.5-7 mm, acute to aristate; awns 5.5-13 mm; anthers to 3.5 mm. Caryopses 2.2-4 mm long, about 1 mm wide. 2n = 36.

Danthonia unispicata is restricted to western North America, where it grows in prairies and meadows, on rocky slopes, and in dry openings up to timberline in the mountains. It differs from D. californica in its shorter stature, usually densely pilose foliage, short, erect pedicels, and the usually erect cauline leaf blades. It is closely related to D. californica, and some authors prefer to treat it as Danthonia californica var. unispicata Thurb.