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Last Updated: Spring 2011

Synonyms: NONE

Family: Asteraceae

Home Range/U.S. Introduction:
Yellow starthistle, native of Eurasia, was introduced into western North America in the mid 1800's and has become naturalized across most of the U.S. Highest densities occur in California, Oregon, Washington, and Idaho.

U.S. Range Map:

Species Description:
Yellow starthistle is a gray-green to blue-green annual or biennial with a deep taproot. The stems are erect, 2-10 dm tall, freely branching, covered with a thin tomentum and prominently winged by decurrent leaf bases. The basal leaves are lyrate or pinnatifid, early deciduous, 4-5 cm wide to 20 cm long; middle and upper leaves are smaller becoming linear and entire. The yellow flowers are in heads that terminate the branches. The middle and outer involucral bracts are spine tipped, the larger central spines commonly 11-30 mm long; inner bracts unarmed. Pappus lacking on marginal flowers, that of others 3-5 mm long. The fruit is a yellowish achene with brown marbling.

Habitat/Growth Characteristics:
The plant develops a deep taproot allowing it to proliferate on dry sites. It reproduces exclusively be seed, estimated to be as high as 29,000 seeds per square meter with about 95% viability. Yellow starthistle frequents fields, roadsides, rangelands, pastures, and waste areas.

Yellow starthistle is a rapid colonizer that can form dense stands. Production of allelochemicals prevents growth of other plant species. It is poisonous to horses, causing the nervous disorder "chewing disease".