cobwebby thistle

Cirsium occidentale

Member of plume thistles (genus Cirsium)
thistles
sunflower family (family Asteraceae)
dicots (class Magnoliopsida)
flowering plants (subphylum Angiospermae)

Except for historical records that I'm ignoring, there are no other wild members of this species in the bay area.
Caution: The key to distinguish these members is not complete.

This species is complex, variable, and not well described. Assigning a variety may not always be possible. My notes are based on a combination of Jepson and Montery County Wildflowers. I’ve mostly ignored CalPhotos because their identifications are all over the place.

venus thistle
Cirsium occidentale var. venustum

heads generally long-peduncled, occasionally in tight clusters at peduncle ends, well elevated above proximal leaves
phyllaries are tomentose, but aren’t significantly interconnected by cobwebby hairs
phyllaries ascending, spreading, or reflexed (the angle of the phyllary’s curve, not the angle that it sticks out of the head)
corolla bright red-pink to red (or rarely other random colors, but generally on the redder side of red-purple)
common everywhere

photo

cobwebby thistle
Cirsium occidentale var. occidentale

heads generally long-peduncled, occasionally in tight clusters at peduncle ends, well elevated above proximal leaves
phyllaries are significantly interconnected by cobwebby hairs
phyllaries ascending to spreading (not reflexed) (the angle of the phyllary’s curve, not the angle that it sticks out of the head)
corolla lavender to bright purple (or rarely white, but generally on the more purple side of red-purple)
common, mostly from the north peninsula to Marin

california thistle
Cirsium occidentale var. californicum

heads short- to long-peduncled in ± open cluster, well elevated above proximal leaves
phyllaries are tomentose, but aren’t significantly interconnected by cobwebby hairs
phyllaries ascending, spreading, or reflexed (the angle of the phyllary’s curve, not the angle that it sticks out of the head)
phyllaries occasionally with sticky-resinous ridge

never sticky on other varieties

corolla pink, pale purple, salmon, or occasionally white/cream
uncommon, mostly around Mt. Diablo

compact cobwebby thistle
Cirsium occidentale var. compactum

heads short-peduncled, closely subtended by basal and large cauline leaves
phyllaries are significantly interconnected by cobwebby hairs
corolla dark rose-purple
very rare near San Bruno Mountain

1 observed taxon / 3 unobserved taxons / 1 key

Chris’s observations: 11 (all are research grade)

Locations:

Henry Coe SP: 4
Sanborn CP: 2
Sierra Vista OSP: 2
Castle Rock SP
Sierra Azul OSP
Sunol Wilderness RP

Months:

Apr.: 1
May: 4
Jun.: 5
Jul.: 1

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Taxon info: iNaturalist – Calflora – CalPhotos – Jepson eFlora – FNA

Bay Area species: iNaturalist – Calflora