15. Paspalum dissectum (L.) L, Fig. 150. 



Long-decumbent mat-forming perennial; culms 20-75 cm. long, compressed, 

 1.5-2 mm. thick on the long axis, freely rooting in the mud, rather freely 

 branched; ligule a membranous scale 1-2 mm. long; blades 2-9 (-12) cm. long, 

 2-5 mm. broad, thin, flat or folded; panicle axis 3-8 cm. long, slender and 

 grooved, 0.2-0.4 mm. thick; racemes 2 to 4, 1-5 cm. long, ascending and slightly 

 arcuate; rachis 1.8-3 mm. broad, with the spikelets borne on a very narrow cen- 

 tral rib, the remainder of the rachis forming foliaceous wings; spikelets solitary, 

 broadly elliptic, 1.7-2 mm. long, 1-1.2 mm. broad, essentially glabrous, greenish 

 to stramineous, apically blunt; first glume absent; fruit blunt. 



Forming mats in moist sand at the margins of seeps, bogs and lakes, on muddy 

 and sandy banks of ponds and ditches or in shallow water, in Okla. (Okfuskee 

 Co.) and e. Tex., infrequent, summer-fall; lowlands of s. U.S., n. to N.J. and 111.; 

 Cuba. 



16. Paspalum fluitans (Ell.) Kunth. Fig. 151. 



Long-decumbent or floating aquatic grasses said to be annual; culms 3-10 dm. 

 long, 2-5 mm. thick, soft (with much gas-holding tissue), mostly submerged, only 

 the floriferous ends emergent; ligule a membranous scale 2-4 mm. long; aerial 

 blades 10-25 cm. long, 9-20 mm. broad, very thin and flat; sheaths pubescent, 

 their corners triangular-auricled; panicle axis 6-16 cm. long, 0.5-1 mm. thick; 

 racemes (20 to) 30 to 50, 25-75 mm. long, ascending or usually arcuate- 

 spreading, at maturity deciduous from the axis; rachis 1-1.7 mm. broad, the 

 spikelets borne on a very narrow central rib, the remainder of the rachis forming 

 thin foliaceous wings; spikelets solitary, 1.2-1.7 mm. long, only about 0.7-0.9 mm. 

 broad, pubescent, pale-stramineous, often with a discolored or stained spot at the 

 base of the sterile lemma and apically acute; first glume absent. P. repens Berg. 



Forming colonies in fresh water, in mud and water on edge of lakes, sloughs 

 and ponds and floating in sluggish streams or standing water, in e. Okla. 

 {Waterfall) and s.e. Tex., infrequent, summer-fall; widespread in trop. Am., n. to 

 N.C., 111., Ind., Mo. and Neb. 



52. Panicum L. Panic Grass 



Annuals or perennials, widely diverse in habit; spikelets in panicles or less 

 commonly in racemes (rarely in spikclike panicles and then sometimes with a 

 bristle-like sterile branch subtending some spikelets); pedicels usually present; 

 each spikelet falling as a unit, 2-flowered, the lower floret staminate or completely 

 reduced, the upper perfect; first glume much shorter than the spikelet, several- 

 nerved, membranous; second glume as long as the spikelet or nearly as long; lower 

 "sterile" lemma several-nerved, membranous, usually as long as the spikelet or 

 essentially so; sterile palea usually obsolete but occasionally (as in P. hians) 

 very strongly developed and cupped and/ or hooded; fertile lemma usually some- 

 what indurate, strongly convex, the margins rcvolute and clasping the palea of 

 the same texture, usually smooth and shining like white cartilage, rarely trans- 

 versely rugose. 



A large extremely complex genus (perhaps 500 species) of warm parts of the 

 world, made particularly difficult in North America because of the occurrence of 

 cleistogamy and occasional wide outcrossing among the "Dichantheliums" or 

 dichotomous panic grasses. 



304 



