Taxon Report

Cirsium hydrophilum (Greene) Jeps. var. vaseyi (Gray) J.T. Howell

Mt. Tamalpais thistle

Print Report

Taxon Summary

Cirsium hydrophilum var. vaseyi, commonly known as Mt. Tamalpais thistle, is a perennial herb in the Asteraceae that is found only in California. It occurs within Broadleafed upland forest, Chaparral, and Meadows and seeps, growing at elevations from 240 to 620 meters. Cirsium hydrophilum var. vaseyi is ranked 1B.2, Plants Rare, Threatened or Endangered in California and Elsewhere; Moderately threatened in California.

Classification


Scientific Name:	Cirsium hydrophilum (Greene) Jeps. var. vaseyi (Gray) J.T. Howell
Common Name:	Mt. Tamalpais thistle
Family:	Asteraceae
Element Code:	PDAST2E1G2
USDA Plants Symbol:	CIHYV
Synonyms/Other Names:

Ecology and Life History


Lifeform:	perennial herb
Blooming Period: May-Aug	May-Aug
Elevation:	240-620 (785-2035)
General Habitats:	Broadleafed upland forest, Chaparral, Meadows and seeps
Microhabitat:	Seeps, Serpentine
Microhabitat Details:

Conservation Status


CA Rare Plant Rank:	1B.2
Global Rank:	G2T2
State Rank:	S2
State List:	None
Fed List:	None
Other Status:	SB_CalBG/RSABG
CRPR Changes:

Occurrence Data from the CNDDB


Total Occurrences:	14
Element Occurrence Ranks:
Excellent (A)	2
Good (B)	6
Fair (C)	0
Poor (D)	0
None (X)	1
Unknown (U)	5

Location


California Endemic: True
California Counties and Islands: Name (Code)
Marin (MRN), San Francisco (SFO)
Quads: Name (Quad Code)
Bolinas (3712286), San Francisco North (3712274), San Geronimo (3812216), San Rafael (3712285)

Threat List Data from the CNDDB


Threat List Total:	6
EOs with Threat Listed:	Total EOs	% of EOs
	9	64 %
Road/trail construction/maint.	5	35%
Foot traffic/trampling	3	21%
Non-native plant impacts	2	14%
Recreational use (non-ORV)	2	14%
Development	1	7%
Other	1	7%

Notes



Known from fewer than 20 occurrences on Mt. Tamalpais. Threatened by road construction and non-native plants. See Synoptical Flora of North America 1(2):403-404 (1884) for original description.
Threats:

Taxonomy:

Selected References

Citation California Native Plant Society, Rare Plant Program. 2025. Rare Plant Inventory (online edition, v9.5.1). Website https://www.rareplants.cnps.org [accessed 7 December 2025].