Cirsium hydrophilum is a species of thistle which is endemic to California, where it is found only in the San Francisco Bay Area and the Sacramento-San Joaquin River Delta. This native thistle grows in wet boggy habitats.

Description

Cirsium hydrophilum may reach 2 m in height with a branching, cobwebby stem. The leaves are longest near the base of the plant, approaching 90 cm in length. They are cut into toothed lobes and covered in spines, particularly along the petiole. The inflorescence bears one or more flower heads, each up to 3 cm long. The head is lined with sticky, twisted, spiny phyllaries and contains pink to purple flowers. The fruit is an achene a 2 - 4 mm long topped with a pappus of about 1.5 cm centimeters.

Varieties

There are two very localized varieties: