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Perennial sowthistle's upper stems produce long flower stalks at their tips. Individual flowerheads are 1-2" in diameter, composed entirely of 80-250 yellow ray florets; disc florets are absent. The fruit, popular with goldfinches, is a flat, dark brown seed with tapered ends, several longitudinal ribs, and a tuft of fine white hairs (like a dandelion). Glandular hairs are typically present on the flower bracts and stalks; if these glandular hairs are absent, glands are present in the epidermis. Perennial sowthistle is indeed a perennial, one with a taproot that may penetrate as deep as 9' into the soil. Of the local sowthistles, perennial sowthistle has by far the largest flowers; other species never exceed 3/4".

Sonchus

Sonchus arvensis

perennial sowthistle [Blooms: Jun-Oct]

Prickly sowthistle's flowerheads are dandelion-like, less than 3/4" in diameter and composed entirely of 80-250 ray florets. Glandular hairs are present on both the flowerhead bracts and on the stalks just below the flowerheads. The fruits are flattened, brown, 2-3 mm long oval seeds with 3-4 ribs per side and a tuft of white hairs on one end. Prickly sowthistle has shiny green (as opposed to the dull green of the other two species) leaves with rounded lobes (as opposed to pointed lobes of common sowthistle) at the base of the leaves. Perennial sowthistle (Sonchus arvensis) has larger (1-2" as opposed to <3/4") flowers and small, rounded lobes at the base of the leaves. The triangular lobes on the base of the leaves of common sowthistle (Sonchus oleraceus) are not found in the other two species.

Sonchus

Sonchus asper

prickly sowthistle [Blooms: Jun-Oct]

Common sowthistle flowerheads are less than 3/4" in diameter and look very dandelion-like; they open in the morning and close by noon. Each flowerhead consists of numerous (80-250) yellow ray florets; disc florets are absent.

Sonchus

Sonchus oleraceus

prickly sowthistle [Blooms: Jun-Oct]