18 



POACEAE. 



Family 15. POACEAE. GRASS FAMILY. 



Annual or perennial herbs, rarely shrubs or trees; stems (culms) 

 generally hollow; nodes closed; leaves 2-ranked, sheathing, the 

 sheaths usually split to the base on the side opposite the blade; 

 a scarious or membranous appendage (the ligule) borne at the 

 opening of the sheath, rarely obsolete; inflorescence a spike, a 

 raceme or a panicle, consisting of spikelets composed of two to 

 many 2-ranked imbricated bracts; the lowest two (glumes) 

 without flowers or rarely wanting; one or more of the upper 

 (lemma) containing in its axil a flower, which is usually enclosed 

 by a bract-like, generally 2-keeled, awnless organ (paled) opposite 

 the glume and with its back toward the axis (rachilla) of the 

 spikelet; lemma sometimes bearing an indurated thickening 

 (callus) at the base; flowers perfect or sometimes monoecious or 

 dioecious, subtended by 1-3 minute hyaline scales (lodicules) ; 

 stamens 1-6, usually 3; ovary 1-celled, 1-ovuled; styles 1-3, 

 commonly 2 and lateral; stigmas hairy or plumose; fruit a seed- 

 like grain (caryopsis) or rarely a utricle; endosperm starchy. 



Tribe 2. 



Tribe 6. 



Spikelets with one perfect flower. 

 Spikelets with only one flower. 



Rachilla jointed below the glumes which fall 



with the seed. 

 Rachilla jointed above the glumes which do 



not fall with the seed. 

 First two lemmas empty, variously modi- 

 fied, the third with a flower. 

 First lemma flower-bearing. 



Spikelets crowded in two rows in one- 

 sided spikes. 

 Spikelets not in one-sided spikes. 

 Spikelets in two opposite rows. 



Hordeum in Tribe 7. 



Spikelets not in two opposite rows. Tribe 3. 

 Spikelets with a staminate or neutral flower in 



addition to the perfect one. 

 Rachilla jointed below the glumes which fall 



with the seed. 

 Rachilla jointed above the glumes which do 



not fall with the seed. 

 Imperfect flower below the perfect. 



Arrhenatherum in Tribe 4. 

 Imperfect flower above the perfect. 



Holcus in Tribe 4. 

 Spikelets with two or more perfect flowers. 



Spikelets sessile on the rachis; inflorescence a 



spike. Tribe 7. 



Spikelets pedicelled; inflorescence a panicle, 



Tribe 1. PANICEAE. 



PHALARIDEAE. 

 CHLORIDEAE. 



HORDEAE. 

 AGROSTIDEAE. 



Tribe 1. PANICEAE. 



AVENEAE. 



AVENEAE. 



HORDEAE. 



