Lactuca serriola L.
Family - Asteraceae
Stems - To +2m tall, erect, single from the base, glabrous above, typically hispid near the base, glaucous or not, with pure white milky sap, herbaceous, from a taproot, fistulose, typically simple except in the inflorescence.
Leaves - Alternate, sessile, lobed or not, to +/-15cm long, 7cm broad, with a distinct white midrib, glabrous, glaucous, auriculate, clasping. Margins spinulose. Midrib with spines abaxially. Sinuses of lobes rounded. Lobes typically retrorse. Terminal lobe larger than the lateral lobes, acute. Entire leaves typically oblong.
Abaxial surface of leaf.
Inflorescence - Terminal and axillary paniculate clusters of multiple flower heads. Inflorescence to +/-45cm long (tall). Axis of inflorescence glabrous. Each division of inflorescence subtended by a clasping bract.
Involucre - To 9mm tall, 2-3mm in diameter. Phyllaries imbricate, unequal, innermost the longest, subulate, to 8mm long, green to reddish in strong sun, glabrous except for a minute tuft of white hairs at the apex (sometimes), with thin scarious margins.
Ray flowers - Flowers +/-12 per head, fertile. Ligule yellow, 5-notched at the apex, glabrous, 7-8mm long, 2mm broad. Corolla tube whitish, 4mm long, glabrous but with a ring of hairs at the apex. Stamens 5, adnate at the apex of the corolla tube, glabrous, 1.5mm long, pale yellow. Anthers yellow, connate around the style, -1.2mm long, exserted. Style exserted beyond the anthers, pubescent in the apical 1/3, pale yellow, bifurcate. Pappus of many capillary bristles, to 5mm long. Achene in flower beaked, slightly compressed, ovoid, -1mm long. Achene dark brown to black in fruit, beaked, to 4mm long. Beak 4mm long.
Disk flowers - Absent.
Fruits - Brown, flattened, ridged, beaked, with short bristles near tip.
Flowering - June - October.
Habitat - Waste ground, fields, disturbed sites, roadsides, railroads.
Origin - Native to Europe.
Other info. - This weedy species can be found throughout Missouri. The plant is easy to identify because of its pure white sap, prickly leaves, and yellow flowers.
Photographs taken in Ellington, MO., 7-13-03 (DETenaglia); also near Labadie, MO, 7-15-2007 (SRTurner).