250 American Midland Naturalist Monograph No. 4 



separately on the same bushes. The male or staminate heads are borne in 

 slender, nodding clusters or catkins while the female or pistillate heads, borne 

 singly, become spiny bur-like structures which may adhere to fur of animals 

 and thus aid in the dispersal of the seed. 



Field Guide to the Species 



Leaves deeply once-to three-limes divided; burs smooth or sparsely hairy 



1. F. dumosa. 



Leaves merely lobed; burs white-cottony 2. F. eriocenira. 



L White Bur-sage (Franser.a dumosa Gray). — Low, round-topped 

 shrub; branches rigid, the older white, becoming spine-like at the tips; stems 

 and herbage grayish-white with a fine close wool; leaves about I/2 to 1 inch 

 long, deeply and irregularly divided along the sides into several rounded 

 lobes, these often again divided; fruiting heads with long straight spines, these 

 sometimes sparingly hairy. 



Occurrence. — grand canyon, in the canyon. 



2. Woolly Bur-sage (Franseria eriocentra Gray). — Similar to Fran- 

 seria dumosa but the shrubs becoming 3 feet high; leaves egg-shaped to oblong, 

 simple or irregularly divided into broad, shallowly toothed lobes, but not 

 divided to the midrib; burs with long straight spines, covered with long, 

 white hairs. 



Occurrence. — grand canyon, in the canyon: Clear Creek trail above Phantom 

 Ranch. 



Mariola Parthenium, Rubber Plant (Parthenium incanum H. B. K.). 

 — Low shrub about 8 to 12 inches high; leaves mostly basal, oval to elliptic, 

 about ^2 to % inch long, irregularly few-lobed, whitish with a very fine felt; 

 flower heads small, borne in flat-topped clusters at the ends of erect leafless 

 flowering stems; flowers white; petal-like ray flowers very small and inconspicu- 

 ous, scarcely exceeding the involucre, these the only fertile flowers; disk flowers 

 in center not producing seeds; seed-like achenes hairy; pappus of 2 papery 

 awns or scales. 



This is a low inconspicuous shrub with whitish leaves mostly at the base. 

 It belongs to the same genus as the Mexican rubber plant or "guayule" (Par- 

 thenium argentatum) from which rubber is obtained commercially. P. incanum 

 has been used for the production of rubber also, but it is far less valuable 

 than the Mexican species. 4^ 



Occurrence. — grand canyon, in the canyon, 2,500 to 5,000 feet: Kaibah trail 

 along switchbacks below Tip-off ; near Phantom Ranch. 



American Trixis (Trixis calif arnica Kell.). — Bushy shrub 1 to 3 feet 

 high, the stems very leafy up to the flower heads; bark smooth, straw-colored 

 or whitish; leaves narrowly egg-shaped to broadly lance-shaped, % to 2i/2 

 inches long, very finely glandular-hairy, margins not toothed or with few 



49 Wooten, E. O., and Standley, P. C, Flora of New Mexico: Contributions from 

 the United States National Herbarium, vol. 19, p. 699. 1915. 



'2 



