46 POACEAE 



and convolute, densely pubescent with silky hairs, with an obtuse callus at the 

 base, and a deciduous straight awn at the apex. Styles distinct; stigmas plumose. 

 Grain oblong, free, enclosed in the lemma. 



1. E. hymenoides (R. & S.) Rydb. Stem 3-6 dm. high, erect, rigid, smooth; 

 leaf-blades 1.5-3 dm. long, involute, less than 2 mm. wide; panicle 1.5-3 dm. 

 long; branches spreading, flexuose; lower glumes 6-8 mm. long, long-acuminate, 

 with somewhat spreading tips; lemma 4 mm. long, broadly ellipsoid, densely 

 pubescent with white hairs. Eriocoma cuspidata Nutt. Bad lands and sandy 

 places: Sask. Kans. Tex. Calif. Wash.; Mex. Plain Mont. My-Jl. 



21. MUHLENBERGIA Schreb. 



Perennials or annuals. Inflorescence a narrow contracted or open diffuse 

 panicle. Spikelets 1 -flowered; flower perfect. Empty glumes 2, membranous 

 or hyaline, persistent, keeled, acute to short-awned, the second sometimes 3- 

 toothed. Lemma somewhat rigid, enclosing the palet, entire or 2-toothed at the 

 apex, obtuse, acute, or awned. Stamens usually 3. Styles distinct; stigmas 

 plumose. 



Panicle contracted, narrow, spike-like, the short branches rarely spreading. 



Empty glumes awl-shaped; leafy and branched plants, with long rootstocks covered 



by imbricated scales. 

 Lemma not awned; basal hairs not equalling the lemma. 



Empty glumes about equalling the lemma in length, sharp-pointed, about 3 



mm. long. 1. A/, mexicana. 



Empty glumes exceeding the lemma, generally twice as long, awned, about 



5 mm. long. 2. A/, racemosa. 



Lemma distinctly awned; basal hairs equalling the lemma. 3. M. cornata. 

 Empty glumes lanceolate to ovate. 



Second glume not toothed or slightly so. 



Lemma awnless 01 rarely very short-awned. 



Empty glumes more than half as long as the lemma. 



Plant 1.5-7 dm. high; sheaths close; empty glumes acuminate, lance- 

 olate. 

 Lemma scabrous, green or dark. 



Panicle dense, obtuse, 5-10 mm. wide. 4. If. Wrightii. 



Panicle slender and lax, attenuate at the apex, less than 5 mm. 



wide. 5. A/, cuspidata. 



Lemma more or less purplish, sparingly long-hairy. 



6. M. Thurberi. 

 Plant less than 1.2 dm. high; sheaths loose; lower leaves lanceolate, 



short, squarrose; empty glumes ovate, acute. 7. M. squarrosa. 

 Empty glumes less than half as long as the lemma, obtuse or abruptly 



acute. 



Spikelets (excluding the awn if present) 1.5 mm. or more long. 

 Plant with a strong perennial, scaly rootstock. 



Empt\ glumes less than one-fourth as long as the lemma; stem 

 diffuse, decumbent or creeping; plant not tufted. 



8. A/. Schrebcri. 

 Empty glumes one-third as long as the lemma or longer; stem 



erect or decumbent at the base only; plant tufted. 



9. A/. Richardsonis. 

 Plant annual ; rootstock, if any, very slender. 



Lemma merelj awn-pointed, decidedly purplish; plant 1-2 dm. 



high. 

 Spikelets 2 mm. long or more; inflorescence short and rather 



dense; stem 0.5-1 mm. thick. 10. A/, simplex. 



Spikelets about 1.5 mm. long; inflorescence slender and lax; 



stem very slender, filiform. 11. A/, filiformis. 



Lemma with a distinct awn 0.5-1 mm. long, greenish; plant 



4-6 cm. high. 12. A/, aristata. 



Spikelets about 1 mm. long; plant less than 4 cm. high, annual. 



13. A/. Wolfli. 

 Lemma long-awned. 



Leaf-blades erect, glabrous or minutely scabrous; stem and sheaths glab- 

 rous. 



Lemma glabrous; rootstock short and woody. 14. M. pauciflora. 

 Lemma pubescent on the lower half; rootstock slender, creeping, 



branched. 15. A/, polycaulis. 



Leaf-blades spreading, as well at the stem below the nodes and the sheaths 

 scabrous-puberulent ; lemma pubescent on the lower half; rootstock 

 creeping. 16. A/, curtifolia. 



Second glume sharply 3-5-toothed; flowering glume long-awned; awn at least 



one-half as long as the glume. 



Stem 3-6 dm. high, leafy; panicle 7-12 cm. long; awn 8-15 mm. long. 



17. M. gracilis. 



