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 
purplish... 22.0... 2... eee eee eee eee eee ce eee ec eee nec eeeee 1. P. nana. 
Tall, 60 cm. or more high; 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... eee ence eee eceeeees 2. P. wrightii. 
Heads 8 to 12-flowered; bracts abruptly acuminate, scaberulous on 
the back. 2... ee eee eee eee e eee eeeee 3. P. thurberi. 
1. Perezia nana A. Gray, Mem. Amer. Acad. n. ser. 4: 111. 1849. . 
TyprE LocALITy: Near Chihuahua, Mexico. 
Rance: Western Texas to southern Arizona and southward. 
New Mexico: Cliff; Laguna Colorado; Carrizalillo Mountains; Dog Spring; 
Deming; San Marcial; Organ Mountains; White Sands; Knowles; Nogal; La Luz 
Canyon. Dry plains and hills, in the Lower Sonoran Zone. 
2. Perezia wrightii A. Gray, Pl. Wright. 1: 127. 1852. 
Typr Locauity: ‘On the Rio Seco and westward; also on the Rio Grande, Texas.’’ 
Ranae: 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 thurberi A. Gray, Mem. Amer. Acad. n. ser. 5: 324. 1854. 
Tyre Locatiry: Rocky hills, near Santa Cruz, Sonora. 
RANGE: Southern New Mexico and Arizona, southward into Mexico. 
New Mexico: Dog Spring; San Luis Mountains. 
3. TRIXIS 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 californica Kellogg, Proc. Calif. Acad. 2: 182. f. 53. 1862. 
TyrE LocALiry: Cedros Island, Lower California. 
Rance: 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 staminate 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 few (rarely solitary or none) in the margins. 
Achenes flattened, wing-margined; involucre with 
1 or 2 inner enlarged scarious bracts... .----- 1. Dicorta (p. 632). 
