Fish Lake Thistle

Cirsium clavatum is a polymorphic and variable species.

Biennials or monocarpic or polycarpic perennials, 20–100 cm; taproots sometimes with branched caudices. Stems 1–several, erect or ascending, glabrous or thinly arachnoid-tomentose; branches 0–10+, slender, usually arising in distal ¹/2, ascending. Leaves: blades oblong to oblanceolate or elliptic, 5–40 × 3–11 cm, unlobed and merely spinulose-dentate or more commonly regularly deeply pinnatifid, lobes well separated to crowded, linear to triangular-ovate, ascending-spreading to retrorse, merely spinulose to coarsely dentate or proximally few-lobed, main spines 2–5(–7) mm, slender, abaxial faces green to gray, glabrous or thinly to densely arachnoid-tomentose, sometimes glabrate, often villous with septate trichomes along veins, adaxial green, glabrous; basal usually present at flowering, sessile or petiolate; principal cauline well distributed, proximal usually winged-petiolate, mid sessile, decurrent as spiny wings 1–3 cm; distal cauline ± reduced. Heads few–many, borne singly or clustered in corymbiform, paniculiform, or racemiform arrays at tips of main stem and branches, sometimes also in distal axils not closely subtended by clustered leafy bracts. Peduncles 0–30 cm. Involucres ovoid to campanulate, 1.5–3 × 1–3 cm, glabrous to thinly arachnoid-tomentose and/or villous-ciliate, with long septate trichomes connecting adjacent phyllaries. Phyllaries in 5–6 series, imbricate or subequal, outer green or with maroon to dark brown subapical patch or appendage, linear to ovate, abaxial faces with narrow glutinous ridge that may be concealed by trichomes; outer and middle with bases appressed, apical appendages erect or ascending, ovate to linear-lanceolate or acicular, entire or spinulose to broadly expanded, scarious, and erose-dentate, apical appendages, spines erect or ascending, 1–5 mm, ± flattened; apices of inner sometimes flexuous or reflexed, narrow, flat, entire or ± expanded, scarious and lacerate-dentate. Corollas creamy white to pale pinkish, 16–20 mm, tubes 6.5–9 mm, throats 4–7.5 mm, lobes 4–6 mm; style tips 3.5–5 mm. Cypselae tan to dark brown, 5–6 mm, apical collars not or scarcely differentiated; pappi 14–16 mm.

Cnicus clavatus M. E. Jones, Proc. Calif. Acad. Sci., ser. 2, 5: 704. 1895

Cirsium clavatum, the Fish Lake thistle or fringed thistle, is a North American species of plants in the tribe Cardueae within the family Asteraceae. The species is native to the western United States, the States of Wyoming, Colorado, Utah, Arizona, and New Mexico.

Cirsium clavatum is a biennial or perennial herb up to 100 cm (40 inches) tall, blooming only once before dying. Leaves have thin spines along the edge, much smaller than those of related species. There are several to many flower heads, with white or pale pink disc florets but no ray florets.

Varieties Cirsium clavatum var. americanum (A.Gray) D.J.Keil - Colorado, Utah, Wyoming Cirsium clavatum var. clavatum - Colorado, Utah Cirsium clavatum var. osterhoutii (Rydb.) D.J.Keil - Colorado