POACEAE. 



FAMILY 1. POACEAE. GRASS FAMILY. 



Annual or perennial herbs, or rarely shrub-like or tree-like plants. 

 Stems (culms) usually hollow, the nodes closed. Leaves with a scarious 

 ring (ligule) at the sheath-orifice. Inflorescence of spikes, racemes, or 

 panicles. Spikelets of 2-many 2-ranked imbricate bracts (scales), the 

 upper ones bearing a flower surrounded by a bract-like organ (palet) 

 which is placed with its back to the axis (rachilla), which is often thickened 

 and appears as a hard projection (callus) at the base of the scale. 

 Flowers perfect, staminate, or pistillate. Stamens 1-6, rarely more, 

 usually 3. Fruit sometimes nut-like. The following treatment of the 

 grasses is based on that published in my Flora of the Southeastern United 

 States./. K. S. 



A. Spikelets falling from the pedicel entire (see also nos. 22, 27, 33 of section B), 



naked, or enclosed in bristles or a bur-like involucre, or immersed in the 

 internodes of a readily disarticulating rachis, 1-flowered, or if 2-flowered the 

 lower flower staminate ; no upper empty scales : rachilla not extending beyond 

 the uppermost scale. 

 Spikelets terete or somewhat dorsally compressed ; empty scales manifest : 



hilum punctiform. 

 Flowering scale, and palet, hyaline, thin, much more delicate in structure 



than the thick-membranous to coriaceous empty scales. 

 Spikelets unisexual, the pistillate borne in the lower, the staminate in 



the upper part of the same spike. Tribe I. MAYDEAE. 



Spikelets in pairs, one sessile, the other 

 pedicellate, the former perfect, the latter 

 sometimes perfect, more commonly with 

 a staminate flower, often empty or re- 

 duced to one or two scales, or occasion- 

 ally wanting. 



Flowering scale, at least that of the perfect 

 flower, similar in texture to the empty 

 scales, or frequently thicker and firmer, 

 never hyaline and thin. 



Spikelets much compressed laterally ; empty 

 scales none or rudimentary : hilum linear. 



B. Spikelets with the empty scales persistent, the 



rachilla hence articulated above them (below 

 them in nos. 22, 27, 33, and the spikelet falling 

 entire), 1-many-flowered : frequently the upper 

 scales are empty : rachilla often produced be- 

 yond the uppermost scale. 



Spikelets borne in open or spike-like panicles or 

 racemes, usually upon distinct and often 

 long pedicels. 

 Spikelets 1-flowered. 



Empty scales 4 : palet 1-nerved. 

 Empty scales 2 (rarely 1) : palet 2-nerved. Tribe 

 Spikelets 2-many-flowered. 



Flowering scales usually shorter than the 

 empty ones, the awn dorsal and usually 

 bent. 



Flowering scales usually longer than the 

 empty ones, the awn terminal and straight, 

 rarely dorsal, sometimes wanting. 

 Spikelets in two rows : 



On one side of the continuous axis, forming 



one-sided spikes or racemes. 

 On opposite sides of an axis which is often 

 articulated, forming equilateral spikes. 



Tribe II. ANDROPOGONEAB. 



Tribe III. PANICEAE. 

 Tribe IV. ORYZEAE. 



Tribe 



V. PHALARIDEAE. 

 VI. AGROSTIDEAE. 



Tribe VII. AVENEAE. 



Tribe IX. FESTUCEAE. 



Tribe VIII. CHLORIDEAE. 



Tribe X. HORDEAE. 



TRIBE I. MAYDEAE. 



Fertile spikelets imbedded in the internodes of the thick 

 rachis. 



TRIBE II. ANDROPOGONEAE. 



Racemes singly disposed : apex of the rachis-internodes a 

 translucent cup-shaped, entire or irregularly toothed ap- 

 pendage. 



1. TRIPSACUM. 



2. SCHIZACHYRIUM. 



