13.15 PASCOPYRUM Á. Löve
Mary E. Barkworth
Plants perennial; rhizomatous. Culms 20–100 cm. Leaves basally concentrated; sheaths striate when dry, smooth, usually glabrous, rarely pilose; auricles present; ligules membranous. Inflorescences terminal, distichous spikes, spikelets usually 1 per node, occasionally in pairs at the lower nodes, spikelets at the lower 4–6 nodes often sterile; lowest internodes to 26 mm, 2 times as long as the middle internodes. Spikelets 12–26(30) mm, 1–3 times the length of the internodes, straight, usually ascending, not appressed, with 2–12 florets; disarticulation above the glumes, beneath the florets. Glumes 5–15 mm, 1/2–2/3 the length of the spikelets, usually narrowly lanceolate, stiff, tapering from midlength or below, slightly curving to the side distally, not keeled, 3–5-veined basally, 1-veined distally, apices acuminate; lemmas lanceolate, rounded on the back, acute, mucronate to awned, awns to 5 mm, straight; paleas slightly shorter than the lemmas; anthers 3, 2.5–6 mm. Caryopses 4–5 mm, falling with the lemmas and paleas. 2n = 56. Haplomes St, H, Ns, and Xm. Name from the Latin pascuum, ‘pasture’, and the Greek pyros, ‘wheat’.

Pascopyrum is a North American allooctoploid genus with one species. It combines the genomes of Leymus with those of Elymus. There are no other species that combine these two tetraploid genomes, although there are many species of both Elymus and Leymus in Eurasia and North America.

SELECTED REFERENCES Dewey, D.R. 1975. The origin of Agropyron smithii. Amer. J. Bot. 62:524–530; Gillett, J.M. and H.A. Senn. 1960. Cytotaxonomy and infraspecific variation of Agropyron smithii Rydb. Canad. J. Bot. 38:747–760.

 

1. Pascopyrum smithii (Rydb.) Barkworth & D.R. Dewey
Western Wheatgrass

Culms 20–100 cm, glabrous. Auricles 0.2–1 mm, often purple; ligules about 0.1 mm; blades 2–26 cm long, 1–4.5 mm wide, decreasing in length upwards, spreading, rigid, adaxial surfaces with prominent veins. Spikes 5–17 cm; middle inter-nodes 4.5–11 mm. Spikelets 12–26(30) mm, with 2–12 florets; lowest rachilla internodes in each spikelet 0.8–2 mm long, 0.5–0.9 mm wide at the top. Glumes 5–15 mm, lower glumes usually exceeded by the upper glumes; lower glumes 0.15–0.8 mm wide at 3/4 length; lemmas 6–14 mm, unawned or awned, awns 0.5–5 mm. 2n = 56.

Pascopyrum smithii is native to sagebrush deserts and mesic alkaline meadows, growing in both clay and sandy soils. Pascopyrum smithii is probably derived from a Leymus triticoidesElymus lanceolatus cross (Dewey 1975); it is frequently confused with both. Leymus triticoides differs in usually having 2 spikelets per node and glumes that are narrower at the base. In E. lanceolatus, the leaves tend to be more evenly distributed and the glumes have straight midveins, become narrow beyond midlength, and tend to be wider at 3/4 length (0.35–1.6 mm). In addition, the first rachilla internodes of E. lanceolatus are often longer and narrower (the length/width ratio averaging 2.6, versus 1.8 in P. smithii). No infraspecific taxa of P. smithii are recognized here.