54 POACEAE 



1. Tripsacum dactyloides L. Glabrous, or on the summit of the sheaths and the 

 upper surface of the leaves more or less hirsute. Stems 1-2.5 m. tall, from stout root- 

 stocks ; blades 6 dm. long or less, 1-4 cm. wide : spikes terminating the stem and its 

 branches, single, or at the summit of the stem in 2's-4's, 1-3 dm. long, the lower ^-i 

 pistillate, the remainder staminate, the margins of the excavations in the pistillate portion 

 ciliate, the sinus at the base with long hairs : pistillate spikelets 7-10 ram. long, orbicular- 

 ovate : staminate spikelets 7-10 mm. long, 1.5-2 mm. broad, oblong, the outer 2 scales 

 glabrous or puberulent. 



In swamps or along streams, Rhode Island to Kansas, Florida, Texas, and Mexico. Summer and 

 fall. Gama Grass. 



2. Tripsacum Floridanutn Porter. Similar to the preceding species, but much more 

 slender. Stems from stout rootstocks, 6-10 dm. tall : leaf-blades long and narrow, usually 

 5-8 mm. wide : spikes rather slender, 1.5-2 dm. long, single, tei'minal, never axillary. 



In moist or wet places, peninsular Florida and tlie Keys to Texas. Spring and summer. 



2. IMPERATA Cyr. 



Perennial grasses, with long leaf-blades and long terminal cylindric dense and spike- 

 like panicles. Spikelets 1-flowered, rarely 2-flowered, narrow, in pairs, unequally pedicel- 

 late. Scales 4, thin, hyaline, awnless, the outer 2 empty, pilose, the third scale glabrous, 

 empty or rarely enclosing a palet and staminate tlower, the fourth scale glabrous, subtend- 

 ing a perfect flower and its 2-nerved palet which is truncate and toothed at the apex. 

 Stamens 1 or 2. Styles distinct. Stigmas plumose. 



1. Imperata Brasili^nsis Trin. Stems tufted, 3-8 dm. tall, slender : leaf-sheaths 

 smooth and glabrous ; blades 3 dm. long or less, 3-8 mm. wide, smooth beneath, hirsute 

 above near the base : panicle 6-15 cm. long, 1.5-3 cm. broad, oblong, its branches 1.5-4 

 cm. long, ascending : spikelets about 4 mm. long, the one about equalling, the other about 

 twice as long as its pedicel, the outer 2 scales and the callus densely clothed with hairs, 

 these, as well as those at the summit of the rachis internodes, more than twice as long aa 

 the spikelets. 



In dry soil, southern peninsular Florida. Also in tropical America. Spring and summer. Bra- 

 zilian Blady-grass. 



3. ERIANTHUS Michx. 



Tall perennial grasses, with frequently robust stems arising from thick rootstocks, and 

 with flat leaf -"blades and perfect flowers in open or contracted terminal panicles. Spikelets 

 usually with a basal ring of long hairs, or rarely naked, in pairs at each joint of the artic- 

 ulated and often hairy rachis. Scales 4, the outer 2 indurated, frequently hairy, the re- 

 mainder hyaline, the fourth scale often 2-toothed at the apex, bearing an awn which is 

 straight, spiral, or more or less contorted ; palet small, hyaline. Stamens 3. Styles dis- 

 tinct, elongated. Stigmas plumo.se. Plume Grass. Beard Grass. 



Spikelets with a basal ring of hairs at least J^ its lengtli, the outer 2 scales long- 

 pilose or becoming glabrous. 

 Panicle pale, rarely tinged with purple, the basal hairs much exceeding the 

 usually yellowish white spikelet. 

 Exserted portion of the awn loosely coiled, the included part tightly spiral. 1. E. alopeciiroidea^ 

 Exserted portion of the awn straight, the included portion rarely slightly 



twisted. 2. E. Tracyi. 



Panicle dark, often tinged with purple, the basal hairsTfrom>horter than to ex- 

 ceeding the yellowish brown or dark brown spikelet. 

 Exserted portion of the awn straight. 



Spikelets 6 mm. long or less, equalling or shorter than the basal hairs. 

 Panicle dense and compact, its branches short and erect ; basal hairs 



about as long as the spikelet. 3. E. compacttts. 



Panicle loose and open, its branches long and ascending ; basal hairs 

 much exceeding the spikelet. 

 Internodes of the branches commonly about as long as the spikelets 



which are about ;;^ as long as the basal hairs. 4. E. saccharoides. 



Lower internodes of tiie elongated branches much exceeding the 



spikelets which are about % as long as the basal hairs. .5. E. laxns. 



Spikelets 8 mm. long or more, exceeding the basal hairs. 0. E. brevibarbis. 



Exserted portion of the awn contorted or loosely spiral. 



Spikelets 7.5 mm. long or less ; summit of the stem and panicle-axis gla- 

 brous or sparingly appressed-hirsute. 7. E. conlortus. 

 Spikelets 8-9 mm. long ; summit of the stem and panicle-axis densely ap- 

 pressed-hirsute. 8. E. Snallii. 

 Spikelet naked at the base or with a few short hairs, the outer 2 scales strongly ap- 



pressed-hispid. 9. E. stricUis. 



