10.03 PTILAGROSTIS Griseb.
Mary E. Barkworth

Plants perennial; tightly cespitose, not rhizomatous. Culms 10–60 cm tall, 0.4–1.2 mm thick, erect, glabrous, not branching at the upper nodes; nodes 1, exposed; basal branching intravaginal; prophylls shorter than the sheaths. Leaves mostly basal, not overwintering; cleistogenes not developed; sheaths open for most of their length, glabrous, smooth to somewhat scabrous; auricles absent; ligules 0.2–3 mm, membranous, rounded to acute, glabrous, not ciliate; blades convolute, 0.2–0.6 mm in diameter, apices stiff, flag leaf blades longer than 1 cm. Inflorescences terminal panicles; branches capillary, often flexuous, sometimes straight, glabrous or sparsely hirtellous; disarticulation above the glumes, beneath the floret. Spikelets 3.4–7 mm, with 1 floret; rachillas not prolonged beyond the floret. Glumes subequal, hyaline, mostly purplish, venation not evident, apices rounded to acute; florets slightly shorter than the glumes, terete; calluses 0.1–0.8 mm, blunt, hairy; lemmas thickly membranous, smooth, hairy over the basal portion or throughout, hairs 0.2–0.4 mm, margins flat, not overlapping at maturity, apices lobed, lobes 0.1–1 mm, membranous, apices with a single terminal awn, lemma-awn junction evident; awns 5–30 mm, centric, persistent, once- or twice-geniculate, sometimes weakly so, scabrous or hairy, hairs to 2 mm; paleas slightly shorter to slightly longer than the lemmas, hairy, hairs to 0.5 mm, 2-veined, not keeled over the veins, flat between the veins, veins ending before the apices, apices rounded; lodicules 3, free, membranous; anthers 3, 0.4–3.3 mm, sometimes penicillate; ovaries glabrous; styles 2, white, free to the base. Caryopses 2–5 mm, fusiform, not ribbed. x = unknown. Name from the Greek ptilon, ‘feather’, and agrostis, ‘grass’, a reference to the feathery awn of the type species.
Ptilagrostis is an alpine and subalpine genus of about 9 species. It grows in central Asia and the high mountains of western North America, sometimes in bogs. Its leaves differ from those of most other members of the Stipeae in lacking sclerenchyma pillars or girders. Two species are native to the Flora region.
SELECTED REFERENCES Barkworth, M.E. 1983. Ptilagrostis in North America and its relationship to other Stipeae (Gramineae). Syst. Bot. 8:395–419; Johnston, B.C. 2006. Ptilagrostis porteri (Rydberg) W.A. Weber (Porter’s False Needlegrass): A technical conservation assessment. Species Conservation Project Report. U.S. Department of Agriculture-Forest Service, Rocky Mountain Region, Lakewood, Colorado, U.S.A. 62 pp. http://www.fs.fed.us/r2/projects/scp/assessments/ptilagrostisporteri.pdf.
1. Awns not hairy; panicles loosely contracted 1. P. kingii
1. Awns hairy, hairs on the lowest segment 1–2 mm long; panicles open or loosely contracted 2. P. porteri
1. Ptilagrostis kingii (Bol.) Barkworth [p. 144]
King’s Ptilagrostis, Sierra Ptilagrostis
Culms 15–38 cm tall, 0.4–0.8 mm thick. Basal ligules 1–2 mm, acute; upper ligules to 2.5 mm; blades filiform, about 0.3 mm in diameter. Panicles 6–10 cm, loosely contracted; branches ascending to appressed. Glumes 3–4.5 mm; florets 2.8–4.2 mm; calluses 0.3–0.7 mm; lemmas with 0.1–0.4 mm lobes; awns 10–14 mm, scabridulous, not hairy, weakly once- or twice-geniculate; anthers 0.5–1.5 mm, penicillate. Caryopses 1.5–2.3 mm. 2n = 22.
Ptliagrostis kingii grows along damp streambanks and wet meadows of the Sierra Nevada, at elevations from 2700–3500 m. It differs from most species in the genus in its scabridulous, rather than plumose, awns and short lemma lobes.
2. Ptilagrostis porteri (Rydb.) W.A. Weber [p. 144]
Porter’s Ptilagrostis,
Rocky-Mountain Ptilagrostis
Culms 23–50 cm tall, 0.6–1.2 mm thick. Lower ligules 0.7–1.5 mm; upper ligules to 2.5 mm; blades filiform, 0.3–0.6 mm in diameter. Panicles 7.5–12 cm, open or loosely contracted; branches spreading. Glumes 4.5–6 mm; florets 2.5–4 mm; calluses 0.1–0.8 mm; lemmas with 0.2–0.8 mm lobes; awns 5–25 mm, hairy, hairs on the lowest segment 1–2 mm; anthers 1.2–3 mm, glabrous. 2n = unknown.
Ptilagrostis porteri grows on hummocks of poorly drained wetlands, at 2700–3600 m, in central Colorado. It is often associated with Salix spp. and Deschampsia cespitosa. There are 29 known populations.
The proportion of plants having closed and open panicles varies among the populations; in some populations all or almost all plants have open panicles, in others all or almost all plants have closed panicles (Johnston 2006). Barkworth (1983) treated P. porteri as a subspecies of P. mongolica (Turcz. ex Trin.) Griseb. because of their morphological similarity. They differ ecologically and geographically, P. mongolica sensu stricto growing in rocky alpine habitats of central Asia.