Purple Starthistle
Centaurea calcitrapa
Purple starthistle is a bushy thistle with highly branched
stems and a stout taproot. It can act as an annual, a biennial,
or a short-lived perennial. It first grows a basal rosette and
later produces stems in late spring and summer. The stems
grow up to three feet tall. Purple starthistle reproduces by
seeds that can remain in the soil for three years. The seedhead
falls as a unit near the parent plant, but the seeds can
then disperse via vehicles, heavy machinery, water, and
soil movement, and by clinging to shoes, clothes, tires, and
fur and feathers of animals. Infestations can result in dense,
impenetrable stands.