Taxonomy

Sonchus tenerrimus L., Sp. Pl. 2: 794. 1753.

Common name

Field sowthistle, slender showthistle

Description

Propagule or dispersal unit is the fruit with pappus. Fertile part 2.5-3.5 mm long, 0.5-1 mm wide, in side view widest in upper part (obovoid), +/- straight or conspicuously curved, the upper (apical) end narrowing, in cross-section flattened, basal scar (carpopodium) inconspicuous and undifferentiated, central, rarely off to the side (oblique) or at least asymmetric, beak (=thinner sterile stalk between seed and pappus) absent, wings absent, fruit surface light brown or straw or dark brown, wrinkled, with round protrusions or bumps, rarely smooth (except at cellular level) (by misinterpretation), with no hairs (glabrous) or papillae (small protuberances), thickened margin absent, longitudinal ribs present, 8-15, their surfaces bumpy or notched, with simple straight hairs or papillae (small protuberances).

Pappus type bristles / hairs, pappus elements all +/- similar, rarely clearly differentiated, up to 4-10 mm long, in several rows, pappus elements numerous, persistent, the individual bristles rough / serrated (barbellate), rarely smooth (by misinterpretation), +/- equal width along length, white / translucent.

Notes: The hairs on the longitudinal ribs are so short and conical that they have been scored as both simple straight hairs and papillae. Sonchus oleraceus and Sonchus tenerrimus are difficult to differentiate from their fruits, but the former appears to have fewer (6-8 vs. 8 or more) and more clearly defined longitudinal ribs.

Ecology

Annual to perennial herb, fruits wind-dispersed. Mediterranean areas. Found on disturbed sites, historically often associated with ship ballast in coastal areas.

Native range

Southern Europe, North Africa, Middle East.

Introduced range

United States, Mexico, Australia.

Past interceptions (Australia): origins

Other or unidentified species of the genus from United States, Colombia, Ecuador, Spain, United Kingdom, Belgium, France, Germany, Hungary, Kenya, China, Korea, Japan, Thailand, Malaysia.

Past interceptions (Australia): commodities

Other or unidentified species of the genus from cut flowers, dried herbs (medicinal), fresh fruit, machinery and parts, new vehicles.