Lactuca virosa L.
acrid lettuce
Annual or biennial. Stem erect, branching above, finely grooved, with patent pale spines up to 4 mm long, especially below, (50)-100-280 cm tall. Lvs green; rosette and lower stem lvs tapering to base, with spinous bristles beneath on midrib and often on secondary veins, 8-25-(35) × 5-18 cm, deeply runcinate-pinnatifid to undivided; margins dentate to bristly-ciliate, usually sinuate. Upper lvs often with spinous bristles on midrib, oblong to obovate, often triangularly 3-lobed at apex, with oblong to rounded amplexicaul auricles at base. Infl. diffusely paniculate. Capitula numerous, cylindric. Involucre (11)-13-15 mm long; bracts imbricate, suberect to reflexed at fruiting; outermost bracts ovate to lanceolate, subacute, ?-1/2length of innermost bracts; inner bracts lanceolate to linear, subacute. Florets c. 11/2× length of involucre; corollas erect to erecto-patent, yellow. Achenes very dark brown or black, 5-8-ribbed on each face, obovate, flattened, finely spiny distally on ribs; body 4-5 mm long; beak pale, c. = body. Pappus fine, white.
N.: throughout; S.: Marlborough (Rarangi and Blenheim).
S., W., and C. Europe, Asia, N. Africa 1940
Waste land, pasture, scrub, hill country, forest margins, riverbed, railway land.
Stem lvs of L. serriola tend to be held on their sides whereas those of L. virosa are held flat. Young plants of L. virosa may be distinguished from L. serriola by the shape of their basal lvs, which have a small, rounded terminal lobe and broad lateral lobes which are broader than the sinus between them and toothed on the distal and most of the proximal margins. Basal lvs of L. serriola have a triangular to ovate terminal lobe and narrower lateral lobes which are about as broad as the sinus between them and not toothed (although they may be ciliate) on the proximal margin. Lvs of L. virosa darken markedly on drying whereas those of L. serriola do not.
