Arctium L.

Tutin, T. G., Heywood, V. H., Burges, N. A., Moore, D. M., Valentine, D. H., Walters, S. M. & Webb, D. A., 1976, Flora Europaea. Volume 4. Plantaginaceae to Compositae (and Rubiaceae), Cambridge University Press : 215

112. Arctium L. 2

Erect biennials, with long, stout taproots. Leaves alternate, tomentose, entire or remotely dentate. Capitula solitary or in corymbose to racemose clusters, ovoid-conical to globose or hemispherical. Involucre glabrous or with arachnoid indumentum; bracts numerous, imbricate, subulate, with appressed bases, the outer long, rigid, patent, with hooked apices. Receptacle flat, with numerous, rigid, subulate scales. Florets tubular, hermaphrodite, purple or white. Anthers acuminate above, sagittate below. Style swollen at base, the branches cuneate. Achenes oblong, compressed, rugose; pappus-hairs scabrid, golden-yellow, free to base.

Specific limits within this genus cannot be clearly defined, each species showing great variation in hairiness ofleaves and capitula, length of peduncles, and colour of capitula and florets. All taxa are interfertile and, although they are normally autogamous, outbreeding sometimes occurs. This has resulted in innumerable intermediates which are fully fertile and breed true from seed.

All species occur in waste places, on roadsides or, occasionally, in woodland.

Literature: J. Arènes, Bull. Jard. Bot. Bruxelles 20: 67-156 (1950).

1 Each main branch of inflorescence corymbose; peduncles 3-10 cm; petioles solid

2 Involucre12 -20x 15 -25mm infruit,withdensearachnoid indumentum, rarely ± glabrous 1. tomentosum 2 Involucre 20-25 x 35-42 mm in fruit, glabrous or subglabrous

2. lappa 1 Each main branch of inflorescence not corymbose; peduncles absent or up to 4 cm; petioles hollow

3 Involucre 15-18 x 15—25 mm in fruit; florets longer than involucral bracts 4. minus 3 Involucre20-25x 30-35mm infruit;floretsaboutaslong

as involucral bracts

4 Involucre straw-coloured; peduncles 1 -4 cm 3. pubens 4 Involucre green or tinged with dark purple; peduncles less than 1 cm 5. nemorosum