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



Spikelets in racemes. 



Racemes short, dense, overtopped by the leaves; spikelets 



awnless 8. Sclerochloa. 



Racemes elongate, loose, exserted; spikelets awned or mu- 



cronate 10. Pleuropogox. 



Spikelets in open or contracted panicles. 



Nerves prominent; plants usually rather tall, growing in 



woods or fresh-water marshes 7. Glyceria. 



Nerves faint; plants low, growing in saline soil. 



6. PUCCIXELLIA. 



Nerves of lemma converging toward the summit, the lemmas 



narrowed at apex. 



Lemmas awned or awn-tipped from a minutely bifid apex 



(awnless in Bromus brizaeformis) ; palea adhering to the 



caryopsis. 



Spikelets in open to contracted panicles; stigmas borne at 



the sides of the summit of ovary 2. Bromus. 



Spikelets nearly sessile in a strict raceme; stigmas terminal 



on the ovary 3. Brachypodium. 



Lemmas entire, pointed, awnless or awned from the tip (mi- 

 nutely toothed in Festuca elmeri and F. gigantea). 

 Spikelets awned (awnless in a few perennial species) ; lem- 

 mas pointed 4. Festuca. 



Spikelets awnless. 



Second glume 5- to 11-nerved; spikelets mostly 1 cm. or 



more long; lemmas broad. 

 Florets persistent on the continuous rachilla, the cary- 

 opsis falling free. 32A. Ectosperma. 



Florets falling together with the joints of the articulate 



rachilla 32. Vaseyochloa. 



Second glume 1- to 3-nerved; spikelets smaller; lemmas 

 5-nerved, membranaceous, not pointed. 

 Spikelets on slender pedicels in compound panicles; 



perennials . 12. Poa. 



Spikelets on thick short pedicels in simple panicles; 

 annual. Rachilla disarticulating at the base, form- 

 ing a stipe to the floret above.... 5. Scleropoa. 



TRIBE 3. HORDEAE 



Spikelets 1- to several-flowered, sessile on opposite sides of a jointed or con- 

 tinuous axis forming symmetrical spikes (not 1-sided, but spikelets sometimes 

 turned to one side in some species) . 



This small but important tribe, found in the temperate regions of both 

 hemispheres, includes our most important cereals, wheat, barley, and rye. 

 The rachis is flattened or concave next to the spikelets, or in some genera is 

 thickened and hollowed out, the spikelets being more or less enclosed in the 

 hollows. In Triticum and its allies there is 1 spikelet at each node of the rachis; 

 in Hordeum and its allies there are 2 or 3 at each node. In Lolium and its 

 allies the spikelets are placed edgewise to the rachis, and the first or inner 

 glume is suppressed except in the terminal spikelet. The rachis of the spikes 

 disarticulates at maturity in several genera. In some species of Elymus and 

 especially in Sitanion the glumes are very slender, extending into long awns, 

 in the latter genus sometimes divided into several slender bristles. The spikes 

 are rarely branched or compound, especially in Elymus condensatus. In this 

 tribe the blades of the leaves usually bear on each side at the base a small 

 appendage or auricle. 



Key to the genera of Hordeae 



la. Spikelets solitary at each node of the rachis (rarely 2 in species of Agropyron, but never 

 throughout). 

 2a. Spikelets 1-flowered, sunken in hollows in the rachis. Spikes slender, cyclindric; low 

 annuals. 



