268 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
49. CENCHRUS L. Sp. Pl. 1049. 1753. 
SAND BUR. BuR GRASS. 
KEY TO THE SPECIES. 
Bristles of bur barbed forwards....................-.222.---.-.-. 2. C. pallidus. 
Bristles of bur barbed backwards. 
Plants perennial; culms woody; spikes long and slender. .... 1. C. myosuroides. 
Plants annual. 
Bristles at base of bur numerous. 
Burs loosely arranged, rather few; spikes usually less 
than 5 cm. long.......... . 5. C. insularis. 
Burs numerous, compactly arranged; ‘spikes often 
more than 5 cm. long. 
Burs about 4 mm. wide; spikes narrowed at the 
summit............. . 3. C. viridis. 
Burs about 6 mm. wide; ‘apikes ‘obtuse ‘at ‘the 
suMMit..........222.-. 22 2--2-222-2--2-2-. 4. C. echinatus. 
Bristles at base of bur few ¢ or none. 
Burs large, 1 to 1.5 cm. wide, the spines often exceed- 
ing 1 cm. in length........................... 8. C. palmeri. 
Burs medium size or small. 
Burs medium size, loosely arranged spines 
slender........... -...-.-.-- 7. C. carolinianus, 
Burs small, compactly ‘arranged, “the spikes 
slender; spines short, usually less than 
3mm. long. ............-.2-.-2..-22202-. 6. C. paucifiorus. 
1. Cenchrus myosuroides H. B. K. Nov. Gen. & Sp. 1: 115. pl. 35. 1816. 
Type locality, ‘‘in arenosis, apricis insulae Cayo Flamingo prope portum Cubensem, 
Batabano,’’ the species also recorded from Patibilca, Peru. 
RanGeE: Florida, Mexico, and the West Indies to South America. 
HERBARIUM SPECIMENS FROM Mexico: 
Lower CaLirornia: Comondt, Brandegee in 1889. 
Sonora: Hermosillo, bank of ditch, Hitchcock 3611; along irrigating ditch, Rose, 
Standley & Russell 12484. Guaymas, Palmer 327 in 1887. Yaqui River, 
Palmer 10 in 1869. 
CuravuanuA: Chihuahua, watercourses, Wilkinson in 1885; wet places, 
Pringle 429. 
DuraNnco: Durango, along a garden wall and beside water ditches, Palmer 
868 in 1896; prairie along creek, Hitchcock 7614. Torreén, along ditch, 
Hitchcock 7560. 
CoaHutta: Saltillo, dry mesa, Hitchcock 5647. 
ZacaTEcas: San Juan Capistrano, Rose 2453. 
AGUASCALIENTES: Aguascalientes, weed, edge of field, Hitchcock 7450. 
Jauisco: Guadalajara, Palmer 765 in 1886. 
Guanajuato: Irapuato, moist sandy-clay plain, Hitchcock 7402. 
Hiaeo: Dublan, valley, Pringle 9598. 
Couma: Revillagigedo Islands, San Benedicto Island, Anthony 370; Barkelew 
171; Socorro Island, Barkelew 202. 
MicHoacdn: El Tibor, prairies, Langlassé 290. 
Puresia: Tehuacan, old field, Hitchcock 6035. 
Oaxaca: Oaxaca, along ditch, Hitchcock 6131. Tomellin, rocky bank by river, 
Hitchcock 6199. 
