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FNA | Family List | FNA Vol. 19, 20 and 21 | Asteraceae | Cirsium

40. Cirsium occidentale (Nuttall) Jepson, Fl. W. Calif. 509. 1901.

Western thistle

Carduus occidentalis Nuttall, Trans. Amer. Philos. Soc., n. s. 7: 418. 1841

Biennials, 5–400 cm; taproots. Stems usually 1, thinly to densely gray- or white-tomentose, sometimes ± glabrate; branches few–many, usually from above mid or near base in compact, moundlike dwarf plants, ascending to spreading. Leaves: blades oblong–elliptic to oblanceolate, 6–40 × 1.5–10+ cm, shallowly to deeply pinnatifid, lobes usually rigidly spreading, undivided or with 1–2 pairs of coarse teeth or lobes, main spines 5–15 mm, both faces gray- to white-tomentose, sometimes ± glabrate or adaxial faces green, thinly arachnoid-tomentose; basal sometimes present at flowering, petiolate or sessile and bases tapered. spiny-winged; principal cauline much reduced distally, sessile, bases decurrent or not, as spiny wings; distal much reduced, linear, ± bractlike. Heads 1–many in loose to tight clusters (barely raised above rosette in dwarf plants). Peduncles 1–30 cm. Involucres ovoid to spheric, 1.5–5 × 1.5–8 cm, arachnoid to ± loosely tomentose, often adjacent phyllaries connected by conspicuous arachnoid trichomes, sometimes glabrous or glabrate. Phyllaries in 7–10 series, subequal to strongly imbricate, green or stramineous to purple-tinged, linear to narrowly lanceolate, abaxial faces without glutinous ridge; outer and mid bodies appressed, entire, apices deflexed to spreading or ascending, short-triangular to elongate, linear-acicular, spines spreading to reflexed, 1–10+ mm; apices of inner erect, often flexuous, flat. Corollas white to lavender, pink, rose-purple, or red, 18–40 mm, tubes 8–18 mm, throats 5–7 mm, lobes 5–10 mm; style tips 4–5 mm. Cypselae ± brown, 5–6 mm, apical collars not differentiated; pappi 15–30 mm.

Varieties 7 (7 in the flora): w United States.

1 Plants compact, rounded, moundlike; heads usually not much elevated above leaves   40c Cirsium occidentale var. compactum
+ Plants usually erect; principal heads usually conspicuously pedunculate   (2)
2 (1) Corollas white to light purple or rose   40d Cirsium occidentale var. californicum
+ Corollas deep purple to bright pink or red   (3)
3 (2) Plants densely white-tomentose; phyllaries persistently white-tomentose (except spines); outer phyllaries usually very long, spreading to reflexed   40g Cirsium occidentale var. candidissimum
+ Plants variably tomentose, sometimes ± glabrate; phyllaries ± arachnoid to floccose-tomentose, sometimes green and glabrate; outer phyllaries short to long, ascending to spreading or reflexed   (4)
4 (3) Involucres usually about as long as wide or wider than long; phyllaries densely and persistently arachnoid with fine trichomes connecting tips of adjacent phyllaries   (5)
+ Involucres usually longer than wide; phyllaries tomentose or glabrate, sparingly or not arachnoid with fine trichomes connecting tips of adjacent phyllaries   (6)
5 (4) Phyllary apices ± imbricate, the proximal usually shorter than medial and distal, lanceolate to linear-acicular, 0.5–15 mm; co- rollas bright purple   40a Cirsium occidentale var. occidentale
+ Phyllary apices subequal, all long- acicular, 1.5–3 cm; corollas light to deep reddish purple   40b Cirsium occidentale var. coulteri
6 (4) Corollas 20–24 mm, deep reddish purple; s Santa Lucia Mountains of San Luis Obispo County, California   40e Cirsium occidentale var. lucianum
+ Corollas 23–35 mm, bright pink to red; widespread   40f Cirsium occidentale var. venustum


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