30 POACEAE. 



5. Cenchrus echinatus L. Sp. PI. 1050. 1753. 



Culms finally prostrate and rooting at the nodes, branched; leaf-sheaths 

 loose; blades 1-4 dm. long, 5-16 mm. wide, smooth or rough, flat; spikes 3-12 

 cm. long, finally more or less exserted; involucres 20-50, containing 4-6 spike- 

 lets, green to purplish, villous at the base, the spines 34 mm. long, the bristles 

 at the base numerous, slender, distinctly barbed for their whole length; spike- 

 lets 6-7 mm. long. 



Sandy soil, waste places and roadsides. Frozen Cay, New Providence, Eleuth- 

 era. Watling*s Island, Fortune Island, Grand Turk and Inagua : Bermuda ; North 

 Carolina to Florida and Texas ; West Indies ; tropical continental America. 

 Southern Bur-grass. 



[Cenchrus hirsutus. Dolley's reference to this name is an error for Cor- 

 choms hirsutus into which he was led by Herrick's misprint of Cenchorus hir- 

 sutus for the same species.] 



18. STENOTAPHRUM Trim Fund. Agrost. 175. 1820. 



Perennial creeping branched grass, with rather stout flattened culms and 

 sh^rt linear leaves. Spikelets spieate or panicled, acute, mostly 2-flowered, 

 imbedded in depressions on one side of the flattened rachis. Scales 4; first 

 scale small or minute, second about as long as the spikelet, third similar to the 

 second, subtending a staminate flower, fourth rigid, enclosing a perfect flower. 

 Stigmas plumose. [Greek, a narrow depression.] A few species of tropical 

 and subtropical distribution, the following typical. 



1. Stenotaphrum secundatum (Walt.) Kuntze, Rev. Gen. 794. 1891. 



Ischaemum secundatum Walt. Fl. Car. 249. 1788. 



Stenotaphrum americanum Schrank,_ PI. Rar. Monac. pi. 98. 1819. 



Widely creeping, sometimes 5 m. long, glabrous, rooting at the lower nodes. 

 Leaf-sheaths keeled, flattened, the blade linear, 3-15 cm. long, 4-10 mm. wide, 

 blunt and rounded at the apex; spikelets about 6 mm. long in spikes 4-13 cm. 

 long. 



Waste places and roadsides, North Bimini, Great Bahama, Abaco, Andros, New 

 Providence, and Fortune Island : Bermuda : South Carolina to Florida and Texas ; 

 West Indies and tropical continental America. Running Crab-grass. 



19. ARISTIDA L. Sp. PI. 82. 1753. 



Grasses varying greatly in habit and inflorescence. Leaves narrow, often 

 involute-setaceous. Spikelets narrow, 1-flowered. Scales 3, narrow, the two 

 outer carinate; the third rigid and convolute, bearing three awns occasionally 

 united at the base, the lateral awns rarely wanting or reduced to rudiments. 

 Palet 2-nerved. Stamens 3. Styles distinct. Stigmas plumose. Grain free, 

 tightly enclosed in the scale. [Latin, from arista, an awn.] About 100 species, 

 in the warmer regions of both hemispheres. Type species: Aristida adscen- 

 sionis L. 



Awns about equal in length. 



First scale shorter than the second. 



Annual : blades thin, flat or involute. 1. A. adscensionis, 



Perennial : blades thick, folded or involute. 2. A. cognata. 



First scale about as long as the second ; perennial. 3. A. gyrans. 



Lateral awns minute. 4. A. scabra. 



