GENERA OF GRASSES OF THE UNITED STATES. 249 



Rarum Adans., Fain. PI. 2: 35, 597. 1763. Of the four pre-Linnsean citations 

 two are given by Linntmis under Ccnclirux echinatus, which is taken as the type. 



Cenchropsis Nash, in Small, Fl. Southeast. U. S. 109. 1903. Cenchrus myosu- 

 roides H. B. K. is designated as the type. 



Nastus Lunell, Amer. Midi. Nat. 4: 214. 1915. The name is ascribed to 

 Dioscorides and " Cenchrus frutescens Linn." given as the type. Lunell intends 

 in apply the name to Cenchrus, but the designated type is unidentifiable and 

 certainly is not a grass. 



Most of the species of the United States are annual. Cenchrus 

 myosuroides H. B. K. differs from our other species in the involucre, 

 or bur, with bristles united only at the base. Were it not for certain 

 species of Australasia which are intermediate, this species might be 

 segregated under a distinct genus, as was done by Nash. 1 The original 

 C. tribuloides L. (fig. 151) is a dune grass of the Atlantic coast, with 

 large villous burs. The common sand bur of the interior found in 

 sandy fields across the continent is C. pauciflorus Benth. This was 

 formerly confused with C. tribuloides and more recently has been 

 called C. carolinianus Walt., which proves to be a different species. 

 Cenchrus echinatus, a common tropical species extending into the 

 Southern States, has a less prickly bur, with a ring of slender bristles 

 at the base of the stout prickles. The species of Cenchrus, especially 

 the last two, are excellent forage grasses before the burs are formed. 

 The genus has been revised by Nash. 2 



127. AMPHICARPON Raf. 



Spikelets of two kinds on the same plant, one in a terminal panicle, 

 perfect but not fruitful, the other cleistogamous on slender leafless 

 subterranean branches from the base of the culm or sometimes also 

 from the lower nodes; first glume of the aerial spikelets variable 

 in size, sometimes obsolete; second glume and sterile lemma about 

 equal; lemma and palea indurate, the margins of the lemma thin 

 and flat; fruiting spikelets much larger, the first glume wanting; 

 second glume and sterile lemma strongly nerved, subrigid, exceeded 

 at maturity by the turgid, elliptic, acuminate fruit with strongly 

 indurate lemma and palea, the margins of the lemma thin and flat; 

 stamens with small anthers on short filaments. 



Annual or perennial erect grasses, with flat blades and narrow 

 terminal panicles. Species two, in the Atlantic Coastal Plain region 

 of the United States. 



Type species: Milium ampMcarpum Pursh. 



Amphicarpon Raf., Amer. Month. Mag. 2 : 175. 1818. In a review of Pursh's- 

 Flora of North America, Rafmesque indicates that Milium amphicarpon should 

 be a new genus, Amphicarpon Raf. Kunth 8 published the genus Amphicarpum, 

 based on the same type, apparently ignorant of Rafinesque's proposed name. 



1 Censhropsis myosuroldcs (H. B. K.) Nash, in Small, Fl. Southeast, U. S. 109. 1903. 



2 Bull. Torrey Club 22: 298-301. 1895. 



3 Rev. Gram. 1: 28. 1829. 



