Sonchus oleraceus is an annual herb, to 1 m tall, from a taproot, mostly hairless, sap milky (but sometimes very weakly so), plant often waxy pale green, somewhat fleshy.
Leaves alternate, initially with a basal rosette that may overwinter, blades irregularly pinnately lobed, lobes toothed, to 30 c long, 15 cm wide, upper leaves often unlobed, margin with few weak prickles, basal lobes pointed, clasping stem, usually pale, waxy-green, lowest leaves stalked.
Flowers pale yellow, 80-250 per head, heads to 2.5 cm wide, all rays, base of flower head (receptacle) becoming wider as fruit (achenes) ripen, basal bracts of flower head narrow, somewhat overlapping, to 1.3 cm high in fruit and becoming hard; inflorescence branched; blooms June-Oct.; Although flowers are self-compatible, insect visitors include solitary bees and syrphid flies (Hutchinson et al. 1984).
Fruit dry, achenes 0.3 cm, flattened, tip narrowed, margin unwinged, 3-5 ribs per side, finely bumpy cross-grained (use lens), with white plume, wind dispersed. Seeds eaten by some birds (Martin et al. 1961). Seeds apparently live only a few years in soil seed bank.
Wetland status: UPL.
Frequency in NYC: Infrequent, probably ephemeral.
Habitat: Open areas, vacant lots, lawns, gardens, fill, roadsides.
Notes: Insects and diseases affecting common sow thistle the same as those for S. asper (above).