About Cirsium cymosum (Greene) J.T.Howell
Cirsium cymosum, commonly called peregrine thistle, is a North American thistle species native to the western United States. It has been recorded in California, Oregon, Nevada, Utah, Idaho, Wyoming, and Montana. This species is a biennial or perennial herb that reaches a maximum height of just 100 cm (39 in). Its surface is covered in a mix of soft and coarse hairs, and sometimes bears cobwebby fibers. Its spiny leaves can grow 30 to 50 centimeters (12 to 20 inches) long, and are largest near the base of the stem. The leaves are deeply divided into lobes edged with sharp teeth. The inflorescence is a cluster of flower heads; each individual head grows up to 3 centimeters long and 5 centimeters wide. The head is lined with sticky, spiny phyllaries and filled with dull white flowers. The fruit is an achene, with a dark-colored body just under one centimeter long, and a pappus of hairs that can reach up to 2.5 centimetres (0.98 inches) in length. Two varieties are recognized: Cirsium cymosum var. canovirens (Rydb.) D.J.Keil, which occurs across most of the species’ full range, and Cirsium cymosum var. cymosum, which is found in California, Nevada, and Oregon.
