Introduced from Europe and now found from the Atlantic to the Pacific coasts, as well as in many other parts of the world in warmer climates.
An annual weed that grows in thick clumps in most settings, such as roadsides, pastures, drainage or irrigation ditches, and waste areas. It survives well in dry areas. Reproduction is from seeds.
This is a very distinctive weed, with long, yellow, 3-forked spines growing along the stems at the base of the leaves, giving this plant a very hazardous personality. Mature plants are bushy due to the extensive branching, and can grow as high as 3 feet.
Leaves are covered with short hairs on their lower surface and the veins on the upper surface stand out as starkly white against the green background. Leaves can be 5 inches long with 2 to 5 large lobes and a short stem, and with the strong spines at their base.
Flower heads are very inconspicuous, composed of small yellowish-green male flowers at the tips of the branches and small groups of female flowers at the base of the leaf stalk. The female flower remains enclosed in the spiny bracts, forming a closed bur about ¾ inch long. The spines are hooked, enabling the bur to break off and be carried easily in animal fur for dispersal of the seeds.
Characteristicts Important to Control:
Seed dispersal is either in the general area of the parent plant or physical dispersal on animals or objects only. Physical removal of individual plants, taking heed of the spines, is effective.