MANUAL OF THE GRASSES OF THE UNITED STATES 



611 



Panicles more or less contracted; spikelets not more than 2.8 mm long. 



153. P. RHIZOMATUM. 



Rhizomes wanting; culms strongly compressed with keeled sheaths; spikelets not 



obliquely disposed. 



Ligule ciliate; basal leaves half as long as the culm or more; panicle much 



exceeding the upper leaves. 



Spikelets not more than 2.7 mm, usually 2.5 mm long, the first glume less 



than half that length; ligule 2 to 3 mm long._ 150. P. longifolium. 



Spikelets 3 to 3.5 mm long; first glume two-thirds to three-fourths that 



length; ligule less than 1 mm long 151. P. combsii. 



Ligule erose or lacerate, not ciliate; basal leaves in short tufts, the upper usu- 

 ally nearly equaling the terminal panicle. 

 Fruit stipitate; spikelets 2.5 to 2.8 mm long, conspicuously secund. 



149. P. STIPITATUM. 

 Fruit not stipitate; spikelets not conspicuously secund. 



Spikelets 1.8 to 2 mm, in occasional specimens 2.2 mm long; panicle 



branches ascending or spreading 147. P. agrostoides. 



Spikelets about 2.5 mm long; panicle branches erect or nearly so. 



148. P. CONDENSUM. 



1 1 . Laxa 

 A single species 154. P. hians. 



12. Verrucosa 



Spikelets about 2 mm long, glabrous 155. P. verrtjcosum. 



Spikelets more than 3 mm long, hispid 156. P. brachyanthum. 



13. Urvilleana 



A single species 157. P. urvilleanum. 



14- Obtusa 



A single species 158. P. obtusum. 



15. Hemitonia 



A single species 159. P. hemitomon. 



16. Gymnocarpa 



A single species 160. P. gymnocarpon. 



Subgenus 1. Paurochaetium Hitchc. and Chase 



Perennials; culms tufted, erect, blades not more than 7 mm wide; 

 panicle slender, the branches short, appressed, the ultimate 

 branchlets bearing 1 to several spikelets, produced beyond the 

 uppermost spikelet as a bristle 1 to 6 mm long; spikelets much 

 swollen on the face, glabrous, strongly nerved; fruit transversely 

 rugose, apiculate. 



1. Panicum chapmani Vasey. (Fig. 1270.) 

 Culms ascending or spreading, slender, wiry, 

 40 to 100 cm tall; blades erect, rather firm, 

 15 to 40 cm long, 2 to 5 mm wide, more 

 or less involute when dry; panicle mostly 

 20 to 30 cm long; bristle 3 to 6 mm long; 

 spikelets 2 to 2.2 mm long, obovate; first 

 glume about one-third as long as the spike- 

 let, obtuse or truncate. 21 — Coral sand 

 and shell mounds, southern Florida; Baha- 

 mas; Yucatan. 



2. Panicum ramisetum Scribn. (Fig. 1271.) Culms erect or as- 

 cending from short horizontal rhizomes, 25 to 60 cm tall; blades 5 to 



Figure 1270. — Panicum chapmani. 

 Panicle, X 1; two views of spike- 

 let, and floret, X 10. (Type.) 



