Time of bloom: June to September.
Seed-time: July to October.
As a weed this plant is most common and troublesome on the Pacific Coast, and it is by means of Californian seed grain that it has found its way into many new localities. It is an arduous task to cleanse the smooth, wedge-shaped achenes from such seed, but less strenuous than fighting the growing weeds.
Stem stout, much branched, one to two feet tall. Flower-heads yellow, which cause it to be often confused with St. Barnaby's Thistle; but it differs from the latter in that its hairy covering is roughish instead of being soft and floccose; also the leaves are but slightly decurrent, the lower ones pinnatifid, the upper ones very narrow and mostly entire. Heads terminal, about a half-inch broad, sometimes in clusters of two or three but often solitary; bracts of the involucre stiff, the inner row terminated with weak, ascending, purplish spines; the intermediate row with short, rigid, divergent spines, about a quarter-inch in length, either simple or with one or two shorter ones at base; and the outer row having very short, palmatifid spines. Achenes light gray, with pappus often in triple rows, the central row longest, the inner and outer ones very short.
The same measures should be used for its control as for St. Barnaby's Thistle.