Arctium L.
Fruticose biennials, not spiny. Hairs both glandular, subsessile, and eglandular, cottony, cobwebby, or felted. Lvs alternate, petiolate, simple. Capitula homogamous, globose or broadly ovoid, in racemes or corymbs. Involucral bracts in several series, linear, imbricate, glabrous or with cobwebby hairs, the outer recurved at fruiting; margins denticulate or glabrous; apex spinous, inwardly hooked. Receptacle flat, with stiff, linear-subulate scales. Florets ⚥, all tubular. Corolla glabrous or glandular, 5-lobed, purplish or white. Anthers acuminate at apex, sagittate at base; filaments glabrous. Style branches linear, cuneate, erect, not appressed. Achenes oblong to obovoid, compressed, rugose; achene insertion basal; pappus hairs in several unequal rows, stiff, pale, scabrid, free to base.
Key
5 spp., Eurasia, N. Africa. Naturalised spp. 2.
The hooked tips of the stiff recurved involucral bracts serve in dispersal of capitula at fruiting. The capitulum may be open or closed at fruiting. The presence or absence of cobwebby hairs on the involucral bracts is of little diagnostic value, as there seems to be a large environmental influence on this character. Also the hairs may be present on young capitula only. The petiole of basal lvs may be hollow or solid; this is best observed in fresh specimens.
The spp. are reported to be largely autogamous and interfertile; hybrids are not uncommon in Europe and perhaps occur here.
