GENERA OF GRASSES OF THE UNITED STATES. 249 
Rarum Adans., Fam. Pl. 2: 35, 597. 1768. Of the four pre-Linnexan citations 
two are given by Linnzus under Cenchrus 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. Midl. Nat. 4: 214. 1915. The name is ascribed to 
Dioseorides and “ Cenchrus frutescens Linn.” given as the type. Lunell intends 
to 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.’ 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. paucitflorus 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.? 
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 Jemma 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 Jemma and palea, the margins of the Jemma 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 amphicarpum Pursh. 
Amphicarpon Raf., Amer. Month. Mag. 2: 175. 1818. Ina review of Pursh’s 
Flora of North America, Rafinesque indicates that Milium amphicarpon should 
be a new genus, Amphicarpon Raf. Kunth* published the genus Amphicarpum, 
based on the same type, apparently ignorant of Rafinesque’s proposed name. 
1 Censhropsis myosuroides (i. B. K.) Nash, in Small, Fl, Southeast, U. S. 109. 19038. 
2Bull. Torrey Club 22: 298-301. 1895. 
*Rey. Gram. 1: 28. 1829, 
