Due to its size, spines and rapid spread, bull thistle (Cirsium vulgare) is considered an aggressive weed or noxious plant. Its seeds are wind dispersed, are viable for over ten years and each plant can produce over 10,000 seeds with a germination rate of 95% resulting in dense patches that resist eradication.
Native to Eurasia, this member of the Sunflower Family (Asteraceae) can now be found throughout most of North America, including Alaska. Its habitat includes pastures, dry meadows, roadsides and disturbed, overgrazed and logged areas.
A biennial, bull thistle arises from a short, fleshy taproot. The one to six foot stem is branched, widely spreading and spiny winged. The leaves are strongly lobed with spines on the margins. The upper side is sparsely prickly above and cottony below. The lower leaves can be as much as sixteen inches long.
Bull thistle flowers are more or less clustered at the terminal ends of the stem branches. Each flower head consists solely of reddish-purple disk flowers surrounded by narrow, spine-tipped phyllaries. The straw colored bull thistle seeds have brown or black lengthwise stripes, a protrusion at one end and are tipped with plume-like hairs.
Because of its spiny nature, bull thistle is considered unpalatable to livestock and wildlife. However a few references (ex: Charles Johnson in a 1993 Forest Service Publication) state that despite the spines the flower heads can be and are eaten by cattle, elk and horses.
The thicker stems of bull thistle are edible when peeled, although peeling the stems is a challenge because of the spines. As a child I would often peel bull thistle stems and eat them. The peeled stems taste like celery and have the crisp texture of jicama. Once you get past the spines, bull thistle is a good trail snack.
This bull thistle plant was photographed in July near the Tule River boat launch (Shasta County CA).