The numerous common names for this genus are perhaps indicative of its wide dis- 

 tribution. The genus consists of about 25 species scattered throughout western North 

 and South America. Only two of these species, X. sarothrae and X. miorocephala, are 

 of importance in the Intermountain area. Other North American species include X. 

 hvaoteveata, X. aalifomica, and X. serothina. 



Matchweed commonly invades depleted ranges and is considered an indicator of over- 

 grazed rangelands. Species in this genus are generally unpalatable and seldom grazed. 

 When eaten in quantity, this plant is more or less poisonous to sheep and goats (Benson 

 and Darrow 1944; Kearney and Peebles 1960). 



Xanthocephalum microcephala Shinners (small headed matchweed^ ^) 



Small-headed matchweed is a many-stemmed subshrub up to 6 dm tall. Its stems and 

 leaves are glabrous and resinous. The leaves are linear-filiform and usually less than 

 1 mm wide. 



Tiny heads, only 3 mm long and 1 to 1 . 5 mm wide, occur singly or are more often 

 arranged in small terminal cyme-like clusters. The heads commonly have 1 to 3 disc 

 flowers. Involucral bracts with yellow tips and prominent hyaline margins surround 

 the heads. * 



Hybridization. --Some authors consider X. microcephala to be a subspecies or variety 

 of X. sarothrae (Benson and Darrow 1944; Harrington 1954) . This species forms a poly- 

 ploid series with chromosome numbers of 2n = 16, 24, and 32 (Solbrig 1971; Kail and 

 Pinkava 1976) . 



Distribution and habitat . --This species occurs between 1,000 and 2,500 meters 

 (3,300 and 8,200 feet) in elevation from Idaho southward to southeastern California, 

 Arizona, New Mexico, Texas, and on into Mexico. It may be associated with the sagebrush, 

 pinyon-juniper, yellow pine, and aspen vegetational types. Type locality is reported 

 as "Saltillo, Mexico" (Abrams and Ferris 1960) . 



Use.- Xanthocephalum microcephala has poisoned large numbers of sheep and cattle 

 under range conditions in Texas. It may cause death in acute cases, but abortion is 

 more commonly the result of poisoning by this species. As long as the animals can find, 

 or are provided with, sufficient supplementary forage, poisoning usually does not occur 

 (Kingsbury 1964) . 



Xanthocephalum sarothrae Shinners (broom snakeweed) 



Broom snakeweed is a subshrub up to 7 dm tall (fig. 58). It has a deep taproot, 

 extensive lateral roots, and a woody crown from which grow numerous, slender, erect, 

 brittle, essentially herbaceous branches. The branches and leaves are green, glabrous 

 to puberulent, and slightly resinous. The leaves are also punctate, linear, 2 to 5 

 cm long, and 1 to 2 mm wide. 



The heads contain from 3 to 8 ray and disc flowers each. Resinous, often green- 

 tipped involucral bracts are arranged in a series of 2 to 4 rows around each head and 

 many appear to be in somewhat vertical ranks. The bracts are 3 to 6 mm long and 2 to 

 3 mm wide. Blooming occurs from May to October. Broom snakeweed has 3,535 seeds per 

 gram (1,605,000 seeds per pound). 



Also known as thread-leaf matchweed. 



64 



