Cirsium hydrophilum var. vaseyi

Mount tamalpais thistle, Mount Tamalpais Thistle

Family: Asteraceae · Type: perennial · Native

Conservation status: CNPS 1B.2

Mount tamalpais thistle is a rare (CNPS 1B.2) California native perennial found in northern San Francisco Bay region on Mount Tamalpais in Marin County, specifically within serpentine seeps at elevations of 300 to 450 meters. Flowering from June to September, this thistle produces purple flowers in heads 3 to 3.5 centimeters long with distinctive, densely clustered blossoms. Growing with stems generally branched in the lower half, it develops erect and robust vegetative structures that support its distinctive flowering heads. Its leaves are likely divided and textured, typical of thistles, with potential serrated edges and a rugged appearance characteristic of serpentine habitat plants. The small fruits are oblong or elliptic, measuring 4 to 5 millimeters in length, completing its reproductive cycle in the unique microenvironment of Mount Tamalpais.

Habitat: Serpentine seeps

Bloom period: Jun-Sep

Elevation: 300-450 m

Bioregions: n SnFrB (Mount Tamalpais, Marin Co.).

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