POACEAE 109 



2. Cenchrus macroc6phalus (Doell) Scribn. Stems at first erect or ascending, later 

 becoming prostrate and branched and forming mats, 3-6 dm. long : leaf-sheaths very 

 loose, glabrous, compressed ; blades flat or complanate, smooth and glabrous, 1 dm. long 

 or less, 4-8 mm. wide : spikes stout, 3-5 cm. long : involucres 5-12, 6-8 mm. broad, en- 

 closing 2 spikelets, pubescent, the spines usually 5-8 mm. long : spikelets not exserted be- 

 yond the involucre. 



Along the seashore, New Jersey to Mississippi. Summer and fall. 



3. Cenchrus gracillimus Nash. Stems erect or ascending, 3-6 dm. tall, simple, or 

 sometimes sparingly branched above, slender : leaf-sheaths but little inflated ; blades com- 

 planate, 5-8 cm. long, about 2 mm. wide, acuminate : spikes finally long-exgerted, 3-5 cm. 

 long, bearing 3-6 distant purplish involucres which are glabrous and with a deeply fur- 

 rowed and glabrous base, the spines purple, 5-6 mm. long : spikelets about 8 mm. long, 

 exserted beyond the involucre from J-.} their length. 



In dry sand in the high pine land region, peninsular Florida. Spring and summer. 



4. Cenchrus echinatus L. Stems finally prostrate and rooting at the nodes, 

 branched : leaf-sheaths loose ; blades 1-4 dm. long, 5-15 mm. wide, smooth or rough, 

 flat : spikes 4-12 cm. long, finally more or less exserted : involucres 20-50, densely crowded, 

 containing 4- 6 spikelets, glabrous, green to purplish, pubescent, villous at the base, the 

 spines 3-4 mm. long, the bristles at the base numerous, slender, distinctly barbed for their 

 whole length : spikelets 6-7 mm. long, exserted from the involucre. 



In sandy places, North Carolina to Florida and Texas. Also in tropical America. Spring to fall. 



5. Cenchrus inc6rtus M. A. Curtis. Stems at first erect or ascending, finally pros- 

 trate and rooting at the lower nodes, 3-6 dm. long : leaf-sheaths compressed, inflated ; 

 blades glabrous, flat, 4-15 cm. long, 3-5 mm. wide : spikes usually exserted, 3-6 cm. long : 

 involucres 8-20, containing 2 spikelets, pubescent, ovoid, glabrous at the base, the spines 

 about 3 mm. long, very broad at the base, ciliate : spikelets 5 mm. long, exserted from the 

 involucre. 



In dry sandy places, South Carolina to Florida and Texas. Summer and fall. 



37. CENCHROFSIS Nash. 



Perennial grasses, with long rootstocks, flat leaf -blades and terminal spicate inflores- 

 cence. Spikelets single, subtended by an involucre consisting of 1 or 2 outer rows of 

 barbed bristles which are thickened at the base, and 1 or 2 inner rows of barbed spines 2-4 

 times as long as the bristles and about equalling the spikelet, the involucre articulated to 

 the rachis and readily deciduous. Scales 4, the first and second empty, the first about one- 

 half as long as the spikelet, the third scale longer than the second, enclosing a palet one- 

 half its length or less, the fourth scale chartaceous, firmer, enfolding a palet of similar 

 texture and a perfect flower. Stamens 3. Styles often connate at the very base. 



1. Ceiichropsis myosuroides (H.B.K. ) Nash. Stems 6-14 dm. tall, from a stout 

 rootstock, simple, or branched above : leaf-sheaths glabrous ; blades glabrous, 1-3 dm. 

 long, 3-8 mm. wide : spikes 5-20 cm. long, included at the base or exserted : involucres 

 numerous, consisting of 1-2 rows of barbed spines as long as the single spikelet, and sub- 

 tended by 1-2 rows of barbed bristles }- as long : spikelets about 5 mm. long. [Cenchnt* 

 myosuroides H.B.K.] 



In dry sandy places, Georgia and Florida. Also in tropical America. Spring to fall. 



38. PENNISETUM Pers. 



Annual or perennial, often branched, grasses, with flat leaf-blades and terminal dense 

 cylindric spikes. Spikelets in l's-3's, 1-2-flowered, subtended by an involucre consisting 

 of numerous slender bristles which are not thickened at the base, all the bristles, or at least 

 the middle ones, plumose. Scales 4, rarely 3, the 2 outer empty, the first small or minute, 

 rarely wanting, the second often as long as the spikelet, the third scale empty or enclosing 

 a palet and a staminate flower, the fourth scale firmer, shorter, enfolding a palet of similar 

 texture and a perfect flower. Stamens 3. Styles usually distinct. Stigmas plumose. 



1. Pennisetum setosum (Sw.) Pers. Stems 1-1.5 m. tall, simple or branched : leaf- 

 sheaths glabrous, keeled ; blades 3 dm. long or less, 6-13 mm. wide, long-acuminate, the 

 upper surface toward the base pubescent with long spreading stout hairs : spikes dense, 

 cylindric, 1-3 dm. long, 1-1.5 cm. in diameter: bristles of two kinds, the outer short and 

 slender, merely hispidulous, about as long as or shorter than the spikelet, the inner much 



