Annuals or biennials, taprooted, 15-300 cm, herbage glabrous, puberulent, or slightly tomentose, spiny. Stems erect, usually simple. Leaves basal and cauline; petiolate (basal and proximal cauline) or sessile (distal cauline) ; blades adaxially variegated, margins dentate and often coarsely pinnately lobed, teeth and lobes spine-tipped, glabrous or puberulent. Heads discoid, borne singly, terminal and in distal axils. ( Peduncles with reduced leaflike bracts.) Involucres ovoid to spheric, 15-60 mm diam. Phyllaries many in 4-6 series. unequal, outer and mid with appressed bases and spreading, lanceolate to ovate, spiny-fringed, terminal appendages, at least mid spine-tipped, innermost with erect, flat, entire, spineless apices. Receptacles flat, epaleate, covered with whitish bristles. Florets 25-100+; corollas pink to purple, tubes slender, distally bent, abruptly expanded into short throats, lobes linear; stamen filaments connate. anther bases sharply short-tailed, anther appendages oblong; style branches: fused portions with slightly swollen subterminal nodes, distally cylindric, distinct portions minute. Cypselae ovoid, slightly compressed, not ribbed, apices with smooth, entire rims, glabrous, basal attachment scars slightly angled; pappi falling in rings, outer of many minutely barbed, basally connate, subulate scales, inner of minute smooth bristles. x = 17.
Species 2: introduced; Mediterranean region.
The Genus Silybum is further organized into finer groupings including:
- Species: ZipcodeZoo has pages for 8 species, subspecies, varieties, forms, and cultivars in the Genus Silybum: S. atriplicifolium · S. cernuum · S. eburneum · S. maculatum · S. mariae · S. marianum (Gundagai Thistle (Aust)) · S. marianum 'Adriana' · S. morianum
- David J. Keil "Silybum". in Flora of North America Vol. 19, 20 and 21 Page 66, 82, 83, 164. Oxford University Press. Online at EFloras.org.
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