gray horse-brush, spineless horse-brush Aster (Sunflower) Asteraceae Tetradymia canescens DC
This spring blooming, yellow-flowered, gray tomentose, up to 3 foot tall shrub grows in dry, open places in the foothills. The twigs are densely hairy with less hairy areas beneath each leaf. The 6 to 10 mm long, somewhat cylindric , alternate leaves are closely appressed to the twigs. Clusters of 1 cm long secondary, smaller leaves are in the axils of the 1-3 cm long primary leaves. The flower heads are subtended by 4, rarely 5 thin-margined bracts. There are usually 4 yellow flowers in each head, thus the name Tetradymia (tetra = 4).
Apparently all species of this genus are poisonous to livestock. They produce liver injury in sheep and sensitivity of the skin to sunlight. Symptoms of anorexia, depression, twitching, incoordination, rapid, weak pulse, prostration, dyspnea, coma appear after about 16 hours and cause death within an hour after symptoms appear. Losses of more than 1000 animals in a band are known to occur, especially in the spring when it is one of the few plants with green leaves. Tests have not shown it to be poisonous to cattle, but has been reported to be toxic to horses.

Tetradymia canescens DC. Gray Horse-brush, Asteraceae Sunflower Family
Spineless Horse-brush
CHARACTERISTICS
Unarmed, much-branched shrub 2-5 dm tall
Leaves, involucres, and twigs conspicuously and closely white-tomentose
LEAVES
primary leaves linear or oblanceolate 1-3 cm long& 1-4 mm wide
sometimes bearing axillary fascicles of shorter and proportionately broader leaves
conspicuously, closely, white tomentose
FLOWERS
4 in each head
heads in small cymose clusters terminating the numerous short branches
involucre 7-10 mm high of 4 or sometimes 5 bracts
pappus of numerous white or whitish capillary bristles
FRUIT
densely hairy (rarely glabrous) achenes

HABITAT
dry, open places in foothills and plains

DISTRIBUTION
Southwest Montana and Central Idaho to Oregon and Nevada

OTHER