Carduus in Flora of North America @ efloras.org

12. Carduus Linnaeus, Sp. Pl. 2: 820. 1753; Gen. Pl. ed. 5, 358. 1754.

Plumeless thistle, chardon [From ancient name of thistlelike plant]

David J. Keil

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.

Species ca. 90 (5 in the flora): introduced; Eurasia, Africa.

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. 1988. A biosystematic study of the Carduus nutans complex in Canada. Canad. J. Bot. 66: 1621–1631. 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. 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.

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 3 Carduus nutans

+ 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 (1) Involucres spheric or hemispheric (3)

+ Involucres cylindric or narrowly ellipsoid (4)

3 (2) Corollas 13–20 mm; heads 18–25 mm; involucres 14–20 mm; abaxial leaf faces glabrate except for long, curled, septate hairs along veins 1 Carduus acanthoides

+ 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 2 Carduus crispus

4 (2) Heads 1–5 at ends of branches; phyllaries not scarious-margined, ± persistently tomentose, distally scabrous on margins and faces 4 Carduus pycnocephalus

+ Heads 5–20 at ends of branches; phyllaries scarious-margined, glabrous or spar- ingly tomentose, distally ciliolate or glabrous 5 Carduus tenuiflorus

Lower Taxa