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SONCHUS Linnaeus Sp. Pl.. 2: 793. 1753.

Sow-thistle [Greek sonchos, ancient name for a kind of thistle]

Philip E. Hyatt,

Annuals, biennials, or perennials [shrubs], 3–350+ cm; taprooted, rhizomatous, or stoloniferous. Stems erect, branched distally or throughout, usually glabrous, sometimes stipitate-glandular (mostly distally). Leaves basal and cauline or mostly cauline; basal usually petiolate (petioles usually winged), cauline often sessile; blades mostly oblong, oblanceolate, or lanceolate, (bases often auriculate) margins usually 1(–2)-pinnately lobed, ultimate margins usually dentate (teeth often ± prickly), sometimes entire. Heads borne in corymbiform to subumbelliform arrays. Peduncles not notably dilated distally, usually ± bracteolate, glabrous or stipitate-glandular and/or tomentose. Calyculi 0. Involucres campanulate to urceolate, 5–15+ mm diam. Phyllaries 27–50 in 3–5+ series, unequal, green, deltate to lanceolate or linear, margins sometimes narrowly scarious (sometimes ciliate), apices acute (faces glabrous or stipitate- to setose-glandular). Receptacles flat to convex, ± pitted, glabrous, epaleate. Florets [30–]80–250[–450+]; corollas yellow to orange (not deliquescent; anthers yellowish to brownish apically). Cypselae stramineous or reddish to dark brown, ± compressed, mostly oblong or oblanceoloid to ellipsoid, beaks 0, ribs usually 2–4(–5+) on each face, faces sometimes transversely rugulose or tuberculate, glabrous; pappi tardily falling or persistent, of 80–100+, white, smooth or barbellulate bristles (some flattened, ± setiform scales), outer usually distinct in ± 1 series, inner basally coherent or connate, in 2–3+ series. x = 9.

Species 50–60+ (5 in the flora):Europe (Mediterranean); w Asia; n Africa; Atlantic Islands; some species introduced nearly worldwide.;

Sonchus species are herbs in North America; some are sometimes woody at bases.
Boulos, L. 1973. Révision systématique du genre Sonchus L. s.l.: IV. Sous-genre: 1. Sonchus. Bot. Not. 126: 155–196.

1. Leaf base auricles often recurved or curled, rounded; ligules shorter than tubes; cypselae strongly compressed, ± winged, ribs 3 on each face, faces not rugulose or tuberculate; annuals or biennials 2. Sonchus asper
1. Leaf base auricles usually straight, sometimes curved, obtuse or acute; ligules shorter or longer than tubes; cypselae weakly compressed, ribs 2–5+ on each face, faces transversely rugulose or tuberculate; annuals, biennials, or perennials. (2.)
2. Annuals or biennials; stem bases soft to hard, herbaceous, often hollow. (3.)
3. Leaf blade lobes ± deltate to lanceolate (not constricted at bases), the terminal usually larger than laterals; ligules ± equaling tubes; widespread 3. Sonchus oleraceus
3. Leaf blade lobes ± rhombic to lanceolate (constricted at bases) or ± linear, the terminal ± equaling laterals; ligules longer than tubes; occasional, mostly historic on ballast 5. Sonchus tenerrimus
2. Perennials; stem bases hard, sometimes ± woody. (4.)
4. Cauline leaf base auricles rounded; cypselae dark brown, 2.5–3.5 mm; pappi 8–14 mm; widespread 1. Sonchus arvensis
4. Cauline leaf base auricles acute; cypselae stramineous, 3.5–4 mm; pappi 7–9 mm; Ontario 4. Sonchus palustris