636 MISC. PUBLICATION 200, U. S. DEPT. OF AGRICULTURE 



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 160. P. longifolium. 



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



less than 1 mm. long 161. P. combsii. 



Ligule erose or lacerate, not ciliate; basal leaves in short tufts, the upper usually nearly 

 equaling the terminal panicle. 

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



159. P. STIPITATUM. 



Fruit not stipitate; spikelets not conspicuously secund. 



Sheaths much broader at the summit than the base of the blades, truncate or auricu- 



late 156. P. abscissum. 



Sheaths about as wide at the summit as the base of the blades. 



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



ascending or spreading 157. P. agrostoides. 



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



158. P. CONDENSUM. 



12. Laxa 

 A single species 164. P. hians. 



13. Verrucosa 



Spikelets about 2 mm. long, glabrous, warty 165. P. verrucosum 



Spikelets more than 3 mm. long, hispid 166. P. brachyanthum. 



14- Urvilleana 

 A single species 167. P. tjrvilleanum. 



15. Obtusa 

 A single species 168. P. obtusum. 



16. Hemitonia 

 A single species 159. P. hemitomon. 



17. Gymnocarpa 

 A single species 170. 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 trans- 

 versely rugose, apiculate. 



1. Panicum chapmani Vasey. (Fig. 

 910.) 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, 



Figure 910. — Panicum chapmani. Panicle, X 1; two 

 views of spikelet, and floret, X 10. (Type.) 



obovate; first glume about one-third 

 as long as the spikelet, obtuse or 

 truncate. % — Coral sand and 

 shell mounds, southern Florida; Ba- 

 hamas; Yucatan. 



2. Panicum ramisetum Scribn. 

 (Fig. 911.) Culms erect or ascending 

 from short horizontal rhizomes, 25 to 



