14. Silybum Adanson, Fam. Pl. 2: 116, 605. 1763.
Milk thistle [Greek silybon, a kind of thistle]
David J. Keil
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 (1 in the flora): introduced; Mediterranean region.