248 MISC. PUBLICATION 200, U. S. DEPT. OF AGRICULTURE 



to be of value as soil or sand binders. E. mollis is a natural sea dune 

 grass and E. arenicola and E. flavescens are common on inland shifting 

 dunes; E. triticoides is to be recommended for holding embankments. 

 On the western ranges E. condensatus and E. triticoides are important. 



la. Plants annual; spike long-awned, nearly as broad as long. 



I. E. CAPUT-MEDUSAE. 



lb. Plants perennial; spike much longer than broad. 

 2a. Rhizomes present, slender, creeping. 



Glumes lanceolate, awnless or awn-pointed. Plants of coastal dunes. 



Glumes and lemmas papery, distinctly nerved 2. E. mollis. 



Glumes and lemmas firm, faintly nerved (lemmas nerved at apex). 



3. E. VANCOUVERENSIS. 



Glumes subulate or very narrow. 



Spikelets glabrous; lemmas short-awned 8. E. triticoides. 



Spikelets densely villous to coarsely, sometimes sparsely, pubescent. 

 Lemmas awned or awn-tipped; spike 5 to 15 cm long. 



Lemmas copiously villous; awn 1 to 4 mm long__ 6. E. innovatus. 

 Lemmas hirsute or hirtellous; awn 5 to 10 mm long. 



7. E. HIRTIFLORUS. 



Lemmas awnless; spike 10 to 25 cm long. 



Glumes pubescent; lemmas soft, densely villous 4. E. flavescens. 



Glumes glabrous or nearly so; lemmas relatively firm, coarsely 



pubescent, sometimes sparsely so 5. E. arenicola. 



2b. Rhizomes wanting (or short and stout in E. condensatus). Plants tufted. 

 3a. Rachis tardily disjointing. Glumes and lemmas awned. 



Spike mostly 5 to 7 mm wide; spikelets mostly in twos; blades subin volute. 



15. E. MACOUNII. 

 Spike 8 to 10 mm wide; spikelets often in threes; blades flat, 5 to 10 mm wide. 



16. E. aristatus. 

 3b. Rachis continuous. 



4a. Glumes subulate to subsetaceous, not broadened above the base, the 

 nerves obscure except in E. villosus. 

 Lemmas awnless or awn-tipped, the awn shorter than the body. 



Spike thick, sometimes compound ; spikelets commonly in twos to fours. 



II. E. CONDENSATUS. 



Spike slender; some or most of the spikelets solitary at the nodes, the 

 paired spikelets near the middle. 

 Culms numerous in a close tuft, the leaves mostly basal; lemmas 



mostly awnless 10. E. salina. 



Culms few, loosely tufted, the leaves scattered along the usually 

 taller culms; lemmas awn-tipped, the awn 2 to 5 mm long. 



9. E. AMBIGUUS. 



Lemmas awned, the awn as long as the body or longer. 



Awns straight; lemmas about 1.2 mm wide across the back. 



17. E. VILLOSDS. 

 Awns flexuous-divergent; lemmas about 2 mm wide across the back. 



18. E. INTERRUPTUS. 



4b. Glumes lanceolate or narrower, broadened above the base, strongly 

 3- to several-nerved. 

 Glumes relatively thin, flat, several-nerved, not indurate at base. 

 Lemmas sparsely long-hirsute on the margins toward the summit. 



14. E. HIRSUTUS. 

 Lemmas glabrous or scabrous. 



Lemmas awned 12. E. glaucus. 



Lemmas awnless or minutely awn-tipped 13. E. virescens. 



Glumes firm, indurate at base. 



Awns divergently curved when dry; base of glumes not terete. 



19. E. canadensis. 

 Awns straight; base of glumes terete. 



Glumes about 1 mm wide about the middle, the bases not bowed out. 



20. E. riparius. 

 Glumes 1.5 to 2 mm wide about the middle, the bases bowed out. 



21. E. VIRGINICUS 



1. Elymus caput-medusae L. (Fig. 478.) Annual; culms ascend- 

 ing from a decumbent, branching base, slender, 20 to 60 cm tall; blades 



