Cirsium hydrophilum
Suisun thistle
(c) Arvel Hernandez, some rights reserved (CC BY), uploaded by Arvel Hernandez · licence
Family: Asteraceae · Type: Herb · Native
Cirsium hydrophilum (Suisun thistle) is a native California herb in the Asteraceae family, recognized by 50 congeners; tall (to 2.2 m) tidal-marsh endemic of Suisun Marsh (Solano) + Mount Tamalpais (Marin).
Suisun thistle is a rare California native perennial found in marsh and wetland habitats at low elevations. Flowering from June to September, this plant produces pale rose-purple flowers in heads 1.5 to 2.5 centimeters wide, with delicate clusters emerging from cobwebby stems. Growing up to 2.2 meters tall with an upright habit, the thistle develops a complex branching structure that becomes increasingly glabrous with age. Its leaves are distinctive, with lower leaves spanning 3 to 9 decimeters and featuring deeply lobed edges marked by spiny margins, while upper leaves become progressively smaller and more clasping. The plant's phyllaries are graduated and minutely spiny-fringed, with spreading tip-spines adding to its intricate architectural form.
Identification and appearance
Key characters: 50 congeners; tall (to 2.2 m) tidal-marsh endemic of Suisun Marsh (Solano) + Mount Tamalpais (Marin)
How to tell it apart
vs Carduus: Cirsium has fluffy, feathery seed tufts; Carduus has rough bristles or no pappus and continuous spiny wings down the stem.; vs Silybum: Cirsium leaves are plain green; Silybum has bright white marbling along the leaf veins.; vs Sonchus: Cirsium has thistle-type flowers with spine-tipped bracts; Sonchus has dandelion-like flowers and milky sap.; vs Cynara: Cirsium heads are 1-6 cm across; Cynara heads are massive (4-15 cm, tennis ball sized) with fleshy bases.; vs Centaurea: Cirsium has linear bracts without appendages; Centaurea bracts have fringed or comb-like tips.
Frequently asked questions
Is Cirsium hydrophilum native to California?
Yes. Cirsium hydrophilum is native to California (recorded as native).
What plant family does Cirsium hydrophilum belong to?
Cirsium hydrophilum is in the Asteraceae family, genus Cirsium.
Related species
Other California species in the same genus, family, or bioregion.
Sources: Jepson eFlora · Index of California Plant Names · CalPhotos
Last updated 2026-10-07
Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, Cal-IPC, and more.