28 



CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



the branchlets bearing 1 to 3 short-pediceled spikelets, the setiform prolongation of the 

 axis usually about as long as the spikelets, sometimes twice as long; spikelets 3 to 3.2 

 mm. long, 1.7 to 1.8 mm. wide, obo- 

 vate, subacute, turgid, strongly nerved; 

 first glume clasping, half the length 

 of the spikelet, pointed, 5 to 7- 

 nerved; second glume and sterile 

 lemma subequal, scarcely covering the 

 fruit, 5 to 7 -nerved, the glume ob- 

 scurely reticulated toward the summit; 

 fruit 2.7 to 2.8 mm. long, 1.6 to 1.7 mm. 

 wide, obovate-elliptic, abruptly acute, 

 very turgid. 



Type U. S. National Herbarium no. 

 592755, collected May 27, 1904, Elsordo : 

 (no. 6446). 



This species resembles P. ramisetum, from which it differs in the larger spikelets, 

 usually longer setae, broader, more or less ciliate blades, and markedly knotty rootstock. 



DISTRIBUTION. 



Sandy prairies, southern Texas. 

 Texas: Elsordo, Griffiths 6446; Sarita, Hitchcock 3866; without locality, Nealley. 



TRUE PANICUM. 



Fig. 10.— Distribution of P. firmulum. 

 Zapata County, Texas, by David Griffiths 



SYNOPSIS OF GROUPS. 



Inflorescence consisting of several spike-like racemes along a 

 main axis; fruit transversely rugose. 

 Perennials; culms spreading or creeping; spikelets gla- 

 brous Geminata (p. 30). 



Annuals; spikelets pubescent or glabrous Fasciculata (p. 35). 



Inflorescence an open or contracted panicle, or if with race- 

 mose branches fruit not transversely rugose. 

 Annuals; panicles open, usually diffuse. (See also Laxa 

 and P. costaricense no. 76.) 

 Spikelets glabrous, not warty nor rugulose; fruit pol- 

 ished. 

 First glume less than one-fourth the length of the 

 spikelet, obtuse or truncate; sheaths glab- 

 rous except in P. bartowense Dichotomiflora 



(P- 47). 

 First glume nearly half the length of the spikelet 

 or more; sheaths hispid (sometimes glab- 

 rous in P. decolorans and P. stramineum). .Capillaria (p. 54). 

 Spikelets warty, rugulose, or hispid ; fruit not polished, 

 margins of lemma not inrolled. 

 Spikelets 2 mm. or more long; not tropical species. Verrucosa (p. 126). 

 Spikelets not over 1.4 mm. long; tropical species. Trichoidia (p. 129). 

 Perennials (two species in Laxa annuals). 



Fruit transversely rugose (very faintly so in P. ple- 

 num)) spikelets ellipsoid, glabrous; plants 



robust Maxima (p. 78). 



Fruit not transversely rugose. 



Spikelets densely silky- villous, 6 to 7 mm. long; 



lemma silky on the margins Urvilleana (p. 132). 



