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Prepared by Richard W. Spjut
Ageratina occidentalis (Eupatorium occidentale Hooker 1833) R.M. King & H. Robinson 1970. Western snakeroot. Mostly erect herbaceous stems arising from a branched woody base; leaves opposite below and alternate above the mid region on petioles 5–12 mm long, triangular in outline, thin, veiny, with three main veins radiating (digitately) from the base, toothed along margins to below the middle, with surface (sessile) glands on the lower face; flowering Jul–Sep; flowers pink, or less often white with purplish tinge, 9–21 in a head, the subtending involucral bracts 3–5 mm long, nearly linear, slightly dilated above mid region then acutely tapered to a sharp point, greenish and glandular. Fruit a cypsela, the pericarpium fusiform, 3.5–5 mm long, 5 ribbed, terminating with numerous minutely barbellate white capillary bristles about as long as the flower. Montane rocky places above 4,800 ft, from Central Washington to western Montana south through Idaho, Nevada and southern California. Type from the low hills between the north and south branches of Lewis and Clarke's River, northern ID. Kern Co.: Known from Piute Mt, collected by Wallace and Zigmond, Jul 1928, and later by Shevock (Inspiration Point Botanical Area).