GENERA OF GRASSES OF THE UNITED STATES. 163 



Type 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, 8. 

 stipoides, is included. In this the lateral awns are obsolete. 



Chaetaria Beauv., Ess. Agrost. 30, pi. 8, f. 5, 6. 1812. Twenty-five species 

 are listed, two, C. stricta (based on Ari-stida 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 Rat, 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. schiedeanaTr'm. andRupr., 

 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 Rupr., with short neck, A. tuberculosa Nutt., 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 Steud., called dog-town grass, because it is especially 

 abundant on the new soil of prairie-dog communities. Aristida fend- 

 leriana Steud. 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. 



