Cirsium fontinale var. obispoense
Chorro creek bog thistle, San Luis Obispo Fountain Thistle
(c) Madeleine Claire, some rights reserved (CC BY), uploaded by Madeleine Claire · licence
Family: Asteraceae · Type: Herb · Native
Conservation status: CNPS 1B.2 · Endangered
Cirsium fontinale var. obispoense (Chorro creek bog thistle) is a native California herb in the Asteraceae family, recognized by San Luis Obispo Co. serpentine seeps, green to purple stems, moderate spines.
Chorro creek bog thistle is a rare (CNPS 1B.2) California native perennial found in central San Luis Obispo County in serpentine seeps and streams at elevations below 350 meters. Flowering from April to October, this plant produces purple flowers in nodding heads with distinctive green to dark purple phyllaries that have strongly recurved outer bracts. Growing up to 2 meters tall with green to purple stems, it develops dense cobwebby leaves with longer leaf spines measuring 4 to 7 millimeters. Its leaves are densely covered in velvety hairs, with the undersides especially concealed by soft, web-like textures. The plant's flower heads feature intricate phyllary structures with outer bracts that are strongly curved and up to 20 millimeters long.
Identification and appearance
Key characters: 8 sympatric species; San Luis Obispo Co. serpentine seeps, green to purple stems, moderate spines
Habitat and range
Habitat: Serpentine seeps and streams
Elevation: < 350 m
Bloom period
Cirsium fontinale var. obispoense blooms Apr-Oct.
Conservation status
CNPS 1B.2 · Endangered
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 fontinale var. obispoense native to California?
Yes. Cirsium fontinale var. obispoense is native to California (recorded as native).
When does Cirsium fontinale var. obispoense bloom?
Cirsium fontinale var. obispoense blooms Apr-Oct.
What plant family does Cirsium fontinale var. obispoense belong to?
Cirsium fontinale var. obispoense is in the Asteraceae family, genus Cirsium.
Is Cirsium fontinale var. obispoense rare or endangered?
Cirsium fontinale var. obispoense carries California Rare Plant Rank 1B.2, state rank S2.
What habitat does Cirsium fontinale var. obispoense grow in?
Cirsium fontinale var. obispoense grows in Serpentine seeps and streams.
Related species
Other California species in the same genus, family, or bioregion.
Sources: Jepson eFlora · CNPS Rare Plant Inventory · Index of California Plant Names · CalPhotos · CDFW CNDDB
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.