Starthistle / Barnaby's Thistle - Centaurea solstitialis
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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
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".
Links to more information
Website, video, and graphics by Rob Nelson
For more information on this plant or management please contact US Army Corp of Engineers