20 POACEAE. 



rough: panicle usually interrupted below, 1-3.5 dm. long, 2-5 cm. in diameter; 

 bristles 1-3, green, 8-11 mm. long: spikelets elliptic, acute, 2 mm. long. — 

 Everglades. — F. K. 



3. C. macrosperma Scribn. & Merr. Stems 6-12 dm. tall: leaf -blades linear- 

 lanceolate, 1-3 dm. long: panicle 1-2.5 dm. long, 2-4 cm. in diameter, exclusive 

 of the bristles: bristles single, 1.5-3 cm. long, green: spikelets narrowly ovoid, 

 acute, 3 mm. long, the flowering scale acute, narrowly ovoid, finely transverse- 

 rugose. — Hammocks. — F. K. (Bah.) 



4. C. corrugata (Ell.) Scribn. Stems 3-10 dm. tall: leaf-blades narrowly 

 linear, 1-3 dm. long: panicle 0.5—1.5 dm. long, 4-15 mm. in diameter exclusive 

 of the bristles: bristles solitary or rarely 2 at each spikelet, 5-15 mm. long: 

 spikelets ovoid, acute, about 2 mm. long, the fourth scale very strongly trans- 

 versely and coarsely undulate-rugose. — Hammocks and low pinelands. 



20. CENCHEOPSIS Nash. Erect plants with long rootstocks and terminal 

 spicate inflorescence. Spikelets single, the involucre of 1 or 2 outer rows of 

 barbed bristles and 1 or 2 inner rows of barbed spines which are 2—4 times as 

 long as the bristles and about equalling the spikelet. Scales 4. 



1. C. myosuroides (H.B.K.) Nash. Stems 6-14 dm. tall: leaf -blades 1-3 dm. 

 long, 3-8 mm. wide: spikes 5-20 cm. long: involucres numerous: spikelets 

 about 5 mm. long. — Pinelands. — F. K. (Bah., Cuba, A7it.) 



21. CENCHKUS L. Diffuse plants with terminal spikes. Spikelets 2-6, 

 in an involucre of two thick hard valves. Scales 4, awnless.— Sand-bur. 

 Sand-spur. Bur-grass. Cockspur. 



Involucre pubescent. 1. C. caroUnianus. 



Involucre glabrous. 2. C. gracillimus. 



1. C. carolinianus L. Stems 2-6 dm. long, branching: leaf-blades 6-12 cm. 

 long, 4-S nmi. wide: spikes 3-6 cm. long: involucres 6-20, the spines 3—4 mm. 

 long: spikelets 6-7 mm. long, usually not exserted beyond the involucre. — 

 Hammocks. — F. K. (Ber., Bah., Cuba, Ayit.) 



2. C. gracillimus Nash. Stems 3-6 dm. tall, slender: leaf -blades 5-8 cm. long, 

 about 2 mm. wide, acuminate: spikes usually long-exserted, 3-5 cm. long, bear- 

 ing 3-6 distant purplish involucres with a deeply furrowed and glabrous base, 

 the spines purple, 5-6 mm. long: spikelets about 8 mm. long, exserted beyond 

 the involucre one-third to one-half their length. — Pinelands. 



22. STENOTAPHKUM Trin. Creeping, much-branched plants, with ter- 

 minal spikes or spike-like panicles. Spikelets 2- (rarely 1-) flowered, in 2's-4's 

 in short spikes. Scales 4. 



1. S. secundatum (Walt.) Kuntze. Stems compressed: leaf -blades rounded at 

 the apex, usually less than 1 dm. long, 4—10 mm. wide: spikelets 3.5-5 mm. 

 long. — Coastal sand-dunes. — F. K. (Ber., Bah., Cuba, Ant.) — Shore-grass. 



23. ARISTIDA L. Tufted plants with contracted or open panicles, which 

 are sometimes nearly racemose. Spikelets narrow. Scales 3, the outer 2 mem- 

 branous, the third scale narrow, rigid, strongly convolute, often with a promi- 

 nent callus at the base, the generally spreading awns glabrous to plumose. — 

 Poverty-grass or Wire-grass. 



Leaf-blades flat, not villous at the base. 



First scale of the spikelet usually shorter than the second : flowering scale less 

 than '>S) mm. long. 1. A. Chapmaniana. 



First scale of the spikelet usually longer than the 



second: flowering scale over r>.T) long. 2. A. purpurasccns. 



Leaf-blades involute, at least those of the lower ones and 



those of the innovations, densely villous. 3. A. stricta. 



