Annuals or biennials [perennials], 30–200(–400) cm, spiny, ± tomentose, sometimes glabrate. Stems erect, simple to much branched, (spiny-winged). Leaves basal and cauline; petiolate or sessile; blade margins spiny dentate, often 1–2-pinnately lobed, faces glabrous or hairy, eglandular. Heads discoid, borne singly or 2–20 in dense clusters or corymbiform arrays. (Peduncles naked or leafy-bracteate, spiny-winged or not winged.) Involucres cylindric to spheric. Phyllaries many in 7–10+ series, linear to broadly ovate, bases appressed, margins entire, apices ascending to spreading or reflexed, acute, spine-tipped. Receptacles flat, epaleate, bearing setiform scales (“flattened bristles”). Florets several–many; corollas white to pink or purple, ± bilateral, tubes long, slender, throats short, campanulate, abruptly expanded from tubes, lobes linear; anther bases sharply short-tailed, apical appendages oblong; style branches: fused portions with slightly, minutely puberulent, swollen basal nodes, distally papillate or glabrous, distinct portions very short. Cypselae ovoid, slightly compressed, faces smooth, glabrous, attachment scars slightly lateral; pappi persistent or falling in rings, of many minutely barbed, basally connate bristles or setiform, minutely barbed scales (“minutely flattened bristles”). x = 8, 9, 10, 11, 13.

Distribution

Introduced; Eurasia, Africa.

Discussion

Species ca. 90 (5 in the flora).

Selected References

Batra, S. W. T., J. R. Coulson, P. H. Dunn, and P. E. Boldt. 1981. Insects and Fungi Associated with Carduus Thistles (Compositae). Washington. [U.S.D.A. Techn. Bull. 1616.]

Desrochers, A. M., J. F. Bain, and S. I. Warwick. 1988b. The biology of Canadian weeds. 89. Carduus nutans L. and Carduus acanthoides L. Canad. J. Plant Sci. 68: 1053–1068.

Desrochers, A. M. , J. F. Bain, and S. I. Warwick. 1988. A biosystematic study of the Carduus nutans complex in Canada. Canad. J. Bot. 66: 1621–1631.

Franco, J. do A. 1976. Carduus. In: T. G. Tutin et al., eds. 1964–1980. Flora Europaea. 5 vols. Cambridge. Vol. 4, pp. 220–232.

Kazmi, S. M. A. 1964. Revision der Gattung Carduus (Compositae). Teil II. Mitt. Bot. Staatssaml. München 5: 279–550.

Lower Taxa

Carduus acanthoides, Carduus crispus, Carduus nutans, Carduus pycnocephalus, Carduus tenuiflorus

Key

1	Phyllary appendages 2–7 mm wide, usually wider than appressed bases; peduncles often elongate, distally wingless; heads often nodding, usually borne singly or in leafy corymbiform arrays; involucres 20–70 mm diam	Carduus nutans
1	Phyllary appendages 0.5–1.5 mm wide, usually narrower than appressed bases; peduncles short, if present, usually winged throughout or wingless only near tip; heads erect, 1–many, often clustered at branch tips; involucres 7–30 mm diam	> 2
2	Involucres spheric or hemispheric	> 3
2	Involucres cylindric or narrowly ellipsoid	> 4
3	Corollas 13–20 mm; heads 18–25 mm; involucres 14–20 mm; abaxial leaf faces glabrate except for long, curled, septate hairs along veins	Carduus acanthoides
3	Corollas 11–16 mm; heads 15–18 mm; involucres 12–17 mm; abaxial leaf faces sparsely to densely tomentose with fine, nonseptate hairs and often with curled, septate hairs along veins as well	Carduus crispus
4	Heads 1–5 at ends of branches; phyllaries not scarious-margined, ± persistently tomentose, distally scabrous on margins and faces	Carduus pycnocephalus
4	Heads 5–20 at ends of branches; phyllaries scarious-margined, glabrous or spar- ingly tomentose, distally ciliolate or glabrous	Carduus tenuiflorus