Cirsium crassicaule

Slough thistle

Family: Asteraceae · Type: annual · Native

Conservation status: CNPS 1B.1

Slough thistle is a rare (CNPS 1B.1) California native annual found in the San Joaquin Valley in freshwater marshes at elevations below 100 meters. Flowering from March to June, this thistle produces pale rose-purple to white flowers in heads 1.5 to 3 centimeters wide, forming loose flat-topped clusters. Growing 6 to 10 meters tall with a single, openly branched stem that is notably hollow at the base and thinly cobwebby, it develops distinctive spiny characteristics. Its leaves are elliptic to widely oblanceolate, gray-tomentose underneath, with proximal leaves featuring spiny-lobed petioles and blades that are 1 to 2 times lobed with main spines 3 to 8 millimeters long. The fruit is small, measuring 5 to 5.5 millimeters long with a pappus 1.5 to 2 centimeters in length.

Habitat: Freshwater marshes

Bloom period: Mar-Jun

Elevation: < 100 m

Bioregions: SnJV.

Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, Jepson eFlora, Cal-IPC, and more.