GRASSES OF IOWA. 



KEY TO THE TRIBES IN SERIES B. — POACEAE- 



i. Spikelets i-flowered, with or without a simple continuation of the 

 rachilla behind the palea 2 



1. Spikelets 2-many-flowered 5 



2. Spikelets crowded in two (rarely one) rows along one side of a contin- 

 uous rachis forming unilateral spikes, these scattered along a common axis or 

 digitate at the apex of the stem TRIBE X. CHLORIDEAE. 



2. Spikelets not disposed in unilateral spikes • 3 



3. Inflorescence spicate, the spikelets sessile on alternate teeth or notches of 

 the rachis TRIBE XII. HORDEAE. 



3. Inflorescence racemose (not unilateral) or paniculate, occasionally con- 

 tracted and spike-like, or condensed and apparently capitate; spikelets always 

 distinctly pedicellate 4 



4. Glumes five, the first four empty or (in Hierochlce) the third and 

 sometimes the fourth, which are usually very unlike the first and second, with stam- 

 inate flowers; the fifth glume with a hermaphrodite flower, and falling with the 

 third and fourth; palea i-nerved TRIBE VII. PHALARIDEAE. 



4. Glumes three (only one in Coleanthus, or occasionally four in some 

 species of Sporobolus and Muhlenbergia), the first two empty; palea 2-nerved or 

 nerveless, very rarely i-nerved (Cinna) or wholly wanting (Alopecurus and 

 some species of Agrostis) TRIBE VIII. AGROSTIDEAE. 



5. Culms herbaceous, annual; leaf blade continuous with the sheath 6 



5. Culms woody, perennial ; leaf blade articulated with the sheath. 



—TRIBE XIII. BAMBUSEAE. 



6- Spikelets pedicellate, in panicles, spike-like panicles, or racemes, these 

 never unilateral • • • 7 



6- Spikelets sessile, in true spikes, or on very short pedicels in unilateral 

 racemes • 8 



7. Empty glumes generally longer than the first flowering glume; one or 

 more of the flowering glumes awned on the back or from between the teeth of 

 the bifid apex (some cultivated forms excepted) ; awn twisted, usually geniculate, 

 very rarely straight TRIBE IX. AVENEAE. 



7. Empty glumes generally shorter than the floral glume; flowering glume 

 awnless or with from one to many terminal (very rarely dorsal) straight or 

 simply divergent awns TRIBE XI. FESTUCEAE. 



8- Spikelets in unilateral spikes or racemes, these racemes, digitate or fas- 

 ciculate TRIBE X. CHLORIDEAE. 



8. Spikelets inserted on the alternate teeth or notches of the rachis forming 

 equilateral, flattened, or cylindrical terminal spikes. . . .TRIBE XII. HORDEAE. 



Different recent authors have adopted slight modifications in the 

 classification of grasses. 



HACKEL'S KEY TO THE TRIBES. 



A. Spikelets one, rarely two-flowered, lower flowers when present imper- 

 fect; falling from the pedicel entire or together with certain joints of the rachis 

 at maturity. Rachilla not produced beyond the flowers. Internodes between the 

 different glumes or flowers not measureable. 



