54 CONTRIBUTIONS FROM THE NATIONAL HEftBAKIUM. 



the short branchlets appressed along the ascending branches; spikelets 4 to 5 mm. 

 long, lanceolate, acuminate; first glume one-fifth to one-fourth the length of the 

 spikelet, subacute or obtuse, rarely pointed and one-third the length of the spikelet; 

 second glume and sterile lemma subequal, 7 to 9-nerved, the palea of the sterile floret 

 wanting; fruit 3 to 4 mm. long, about 0.8 mm. wide, lanceolate, acuminate, the mar- 

 gins of the lemma above the middle thin and not inrolled. 



This large, succulent, semi-aquatic, apparently annual species, often producing 

 dense masses of roots at the submerged nodes, is readily distinguished from P. dichoto- 

 miflorum by the acuminate fruit. The Mexican specimens cited below have narrower 

 blades than the others and none show the basal portion, but the floral characters agree 

 with the type, except that the fruit is more turgid and less acuminate. 



DISTRIBUTION. 



In ponds and shallow water, West Indies and southern Mexico, south to Argentina. 

 An introduced specimen was collected in North Carolina, "Eastern part of state along 

 seacoast," by McCarthy in 1898. 



Mexico: Near Mexico City, Bourgeau 529, Pringle 6322," 9577.« 



Guatemala: Alta Vera Paz, Goll 35A. 



Cuba: San Antonio, Hitchcock 152; Habana, Leon 335. 



Porto Rico: Fajardo, Sintenis 938. 



Paraguay: Morong 1002 in part. 



Uruguay: Montevideo, Arechavaleta in 1876, without locality, Arechavaleta in 



1892. 

 Argentina: Lagos de la Darsesso, Buenos Aires in 1892, name of collector not 

 given. 



Capillaria. — Annuals; papillose-hispid at least on the sheaths, or rarely glabrous, 

 ligules membranaceous, ciliate, 1 to 3 mm. long; panicles many-flowered; 

 more or less diffuse, often breaking away at maturity and rolling before the 

 wind; spikelets pointed, glabrous, the first glume large and clasping, the 

 fruit often falling from the spikelet before the disarticulation of the latter, 

 smooth and shining, usually olive brown at maturity, the nerves showing as 

 faint pale lines. 

 Panicles more or less drooping. 



Spikelets not over 3.5 mm. long; Mexican species 28. P. sonorum. 



Spikelets 4.5 to 5 mm. long; introduced from Old World . 30. P. miliaceum. 

 Panicles erect. 



Inflorescence elongated, composed of several approximate, 



implicate panicles 31. P. cayennense. 



Inflorescence not composed of approximate nor implicate 

 panicles. 

 Panicles more than half the length of the entire plant. 

 Panicles narrow, usually less than half as broad 



as long 20. P. flexile. 



Panicle as broad as long. 



Spikelets 2 to 2.2, rarely 2.5 mm. long; 



blades not crowded toward the base. 23. P. capillare. 

 Spikelets 3 to 3.3, rarely only 2.5 mm. long; 

 blades usually crowded toward the 

 base 24. P. barbipulvinatum. 



a These numbers were distributed as a variety of P. proli/erum Lam., the varietal 

 name being unpublished. 



