WOOTON AND STANDLEY FLORA OF NEW MEXICO. 631 



KEY TO THE SPECIES. 



Low, 20 cm. high or less; heads solitary, 20 to 30-flowered, the flowers 



puipUsh 1. P. nana. 



Tall, 60 cm. or more liigh; heads corymbose or paniculate, 5 to 12- 

 flowered, the flowers nearly white. 

 Heads 5 or 6-flowered; bracts obtuse or acutish, glabrous on the 



back 2, P. wrightii. 



Heads 8 to 12-flowered; bracts abruptly acuminate, scaberuloua on 



the back 3. P. ihurheri. 



1. Perezia nana A. Gray, Mem. Amer. Acad. n. ser. 4: 111. 1849. 

 Type locality: Near Chihuahua, Mexico. 



Range: Western Texas to southern Arizona and southward. 



New Mexico: Cliff; Laguna Colorado; Carrizalillo Moimtains; Dog Spring; 

 Deming; San Marcial; Organ Mountains; Wliite Sands; Knowles; Nogal; La Luz 

 Canyon. Dry plains and hills, in the Lower Sonoran Zone. 



2. Perezia wrightii A. Gray, PI. Wright. 1: 127. 1852. 



Type locality: " On the Rio Seco and westward; also on the Rio Grande, Texas." 



Range: Western Texas to southern Arizona and southward. 



New Mexico: Mangas Springs; Florida Mountains; Dona Ana Mountains; Organ 

 Mountains; Tortugas Mountain. Dry hills and ravines, in the Lower and Upper 

 Sonoran zones. 



3. Perezia thui'beri A. Gray, Mem. Amer. Acad. n. ser. 6: 324. 1854. 

 Type locality: Rocky hills, near Santa Cruz, Sonora. 



Range : Southern New Mexico and Arizona, southward into Mexico. 

 New Mexico: Dog Spring; San Luig Moimtains. 



3. TBrXIS P. Br. 



Low woody perennial with entire or denticulate alternate lanceolate leaves and 

 corymbose medium-sized heads of yellow flowers; involucres many-flowered, the 

 bracts 8 to 12, equal, in a single series, subtended by a few bractlike leaves; achenes 

 slender, with a tapering summit; pappus yellowish, of capillary bristles. 



1. Trixis califomica Kellogg, Proc. Calif. Acad. 2: 182./. 53. 1862. 



Type locality: Cedros Island, Lower California. 



Range: Western Texas to Arizona and Mexico. 



New Mexico: Black Range; Mangas Springs; Bear Mountains; Dog Spring; near 

 White Water; Dona Ana Mountains; Organ Mountains; Tortugas Mountain; south of 

 Roswell. Rocky canyons and hills, in the Lower and Upper Sonoran zones. 



143. AMBROSIACEAE. Ragweed Family. 



Annual or perennial herbs or shrubs with alternate leaves; flowers small, aggre- 

 gated on a receptacle, surrounded by an involucre, the etaminate and pistillate in 

 the same or separate heads; involucral bracts few, distinct or united, those of the 

 pistillate flowers often nutlike or burlike at maturity or winged; stamens usually 5, 

 distinct; corollas all tubular; ovary- 1-celled; stigmas 2, hairy or brushlike at the 

 apex. 



key to the genera. 



Staminate and pistillate flowers in the same heads, the 



latter lavr (rarely solitary or none) in the margins. 



Achenes flattened, wing- nargined; involucre with 



1 or 2 inner enlarged scarious bracts 1. Dicoria (p. 632). 



