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.
Cirsium clavatum is a polymorphic and variable species.