Flora of North America species comparison

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Cirsium occidentale var. occidentale

Cirsium occidentale var. compactum
Photo is of parent taxon

cobweb thistle, cobwebby thistle
Photo is of parent taxon

compact cobwebby thistle
Habit Plants erect, usually 30–150 cm or taller. Plants compactly branched, forming low rounded mounds, 5–100 cm, densely gray-tomentose.
Leaf

faces usually densely tomentose abaxially, less so and sometimes glabrate adaxially.

faces gray-tomentose or adaxial ± glabrate.
Involucres

usually wider than long, 4–5 cm diam., ± densely and persistently arachnoid with fine trichomes connecting tips of adjacent phyllaries.

wider than long, 5–8 cm diam., densely arachnoid with fine trichomes connecting tips of adjacent phyllaries.
Corollas

± bright purple, usually 25–35 mm.

dark rose-purple, 25–30 mm.
Phyllaries

usually ± imbricate, outer ascending or spreading or reflexed, mid phyllary apices ascending to spreading, straight or distally curved, usually 1–2 cm × 1–2 mm.

imbricate to subequal, outer and mid apices ± spreading, straight, usually 1–2 cm × usually 1–2 mm.
Heads

usually long- pedunculate, sometimes in tight clusters at ends of peduncles, elevated well above proximal leaves.

borne singly or in ± tight clusters, short-pedunculate, closely subtended and often overtopped by basal and large cauline leaves.
2n

= 28, 29, 30.

= 30.

Cirsium occidentale var. occidentale

Cirsium occidentale var. compactum
Phenology Flowering spring–summer (Mar–Jul). Flowering winter–summer (Feb–Jul).
Habitat Coastal scrub, chaparral, oak woodlands, stabilized dunes, roadsides Coastal sea bluffs, dunes in grassland and coastal scrub
Elevation 0–200 m (0–700 ft) 0–50 m (0–200 ft)
Distribution
from FNA
CA
[BONAP county map]
from FNA
CA
[BONAP county map]
Discussion

Variety occidentale occupies a variety of habitats in the coastal zone of southern and central California. Considerable variation occurs from population to population in head size, flower color, and pubescence. It sometimes occurs together with and appears to intergrade with var. coulteri. Where there has been no hybridization, the two may be strikingly dissimilar, but individuals of some populations cannot be assigned with confidence to either variety.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Variety compactum is locally common along the immediate coast of northern San Luis Obispo County and formerly ranged as far north as San Francisco. Populations referable to this race occur on the California Channel Islands and on the mainland in Monterey County. Because of the very narrow ecologic zone occupied by these plants they are particularly vulnerable to habitat loss. Variety compactum is closely related to vars. occidentale and coulteri.

of conservation concern

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 19, p. 137. FNA vol. 19, p. 139.
Parent taxa Asteraceae > tribe Cardueae > Cirsium > Cirsium occidentale Asteraceae > tribe Cardueae > Cirsium > Cirsium occidentale
Sibling taxa
C. occidentale var. californicum, C. occidentale var. candidissimum, C. occidentale var. compactum, C. occidentale var. coulteri, C. occidentale var. lucianum, C. occidentale var. venustum
C. occidentale var. californicum, C. occidentale var. candidissimum, C. occidentale var. coulteri, C. occidentale var. lucianum, C. occidentale var. occidentale, C. occidentale var. venustum
Name authority unknown Hoover: Vasc. Pl. San Luis Obispo Co., 310. (1970)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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