GENERA OF GRASSES OF THE UNITED STATES. 
163 
Tvpe species: Aristida adscensionis L. 
Aristida L., Sp. PI. 82, 1753; Gen. PI., ed. 5, 35. 1754. A single species is 
described. 
Streptachne R. Br., Prodr. Fl. Nov. Holl. 174. 1810. A single species, S. 
stipoides, is included. In this the lateral awns are obsolete. 
Chaetaria Beau v., Ess. Agrost. 30, pi. 8, f. 5, 6. 1812. Twenty-five species 
are listed, two, C. stricta (based on Aristida stricta Michx.) and C. capillaris, 
are illustrated. Aristida stricta (fig. 5) is taken as the type. 
Curtopogon Beauv., Ess. Agrost. 32, 159, pi. 8, f. 7. 1812, The only species 
included is based on Aristida dichotoma L. 
Trixostis Raf., Bull. Bot. Seringe 1 : 221. 1830. A single species, " Aristida 
gracilis" [Ell.], is included. 
Moulinsia Raf., Bull. Bot. Seringe 1: 221. 1830. A single species, "Aristida 
lanosa" Muhl., is included. 
Ortachne Nees, in Seeman, Bot. Voy. Herald 225. 1857. A single species, 
based on Streptachne pilosa H. B. K., is included. 
In one group of the genus the lateral awns are reduced to mere 
points or are entirely absent. Two species of this group (section 
Streptachne) are found in Arizona, Aristida scabra (H. B.K.) Kunth, 
with a curved but not twisted awn, and A. schiedeana Trin. and Eupr., 
with a twisted awn. The former is found also in southern Florida. 
In three species the awn is articulate at base, A. desmantha Trin. 
and Eupr., with short neck, A. tuberculosa Xutt., an annual with a 
slender, twisted neck, and A. calif omica Thurb., a perennial with a 
slender, twisted neck. Aristida dichotoma Michx., a small annual 
with a coiled central awn, is common in the Eastern States. Two 
other annuals are common in the eastern part of our country, A. gra- 
cilis Ell., with the central spreading or reflexed awn less than half 
an inch long, and A. oligantha Michx. (fig. 95), with awns 2 or 3 
inches long. The type species, A. adscensionis L. (A. bromoides 
H. B. K.), has a wide distribution in warm countries and extends 
into the southwestern United States. This is a low annual, usually 
much branched at base, with contracted panicle, the first glume about 
half as long as the second, and awns about one-third of an inch long. 
A common perennial species in the semiarid regions of the West is 
A. longiseta Steucl., called dog-town grass, because it is especially 
abundant on the new soil of prairie-dog communities. Aristida fend- 
leriana Steucl. is an allied species of the same region. The first has 
a long second glume, about four-fifths of an inch long, and awns as 
much as 3 or 4 inches long. The second has a shorter second glume, 
about three-fifths of an inch long, and awns less than 2 inches long, 
and grows in dense tufts with curly leaves crowded at the base of 
the plant. Aristida purpurea Nutt. differs in having slender curved 
pedicels. These species are troublesome when the fruit is ripe, be- 
cause this with its spreading awns becomes detached at maturity and 
is blown about by the wind. These fruits are sometimes scattered 
in vast quantities, the wind hurling them across the plains with the 
sharp-pointed callus in advance. They work their way into the 
wool of sheep and into the nostrils and eyes of all classes of stock. 
