Reproduces only by seed.
Stems erect, to 1 m high, frequently branched above.
Leaves very variable, rosette leaves long-stalked, pinnately compound with a large terminal leaflet (a) and a mixture of large (b) and small (c) leaflets along each side of the central stalk (rachis), leaflets coarsely toothed, hairy and green on both surfaces; stem leaves alternate (1 per node), similar but with shorter stalks, especially towards the top of the stem and each with a pair of green leaflet-like stipules (d) where the leafstalk (e) joins the stem; upper leaves stalkless, sometimes just shallowly toothed or lobed without being divided into leaflets.
Flowers few in widely branching inflorescences, 1 - 2 cm across, with 5 deep yellow to orange-yellow petals, 5 smaller sepals, numerous stamens and pistils in a dense central cluster; at maturity each flower stalk lengthening and the cluster of pistils enlarging into a nearly spherical brown to dark brown head or bur about 2 cm in diameter; each single-seeded pistil (now a fruit or "seed") in the mature bur has a sharply hooked tip (f) which clings to fur, clothes and skin. Flowers from early June to late summer, and the burs persist into late fall or winter.
Yellow avens occurs throughout Ontario in meadows, open woods, pastures, waste areas and roadsides, but is rarely found in cultivated land.
Yellow avens is distinguished in the rosette stage by long-stalked, pinnately compound leaves, each with a large terminal leaflet and irregularly sized and shaped lateral leaflets; and by flowering and fruiting stages, by its variable leaves, its deep yellow to orange-yellow flowers and the brown spherical, bur-like clusters of seeds, each with a long hooked beak that will cling to skin and clothing.
Bur with sharply hooked tip.
Yellow avens plant.
Yellow avens, June in Southwestern Ontario.
Top of yellow avens plant.
Yellow avens leaf with long, smooth stem.
Leaf of yellow avens.
Small leaflets along each side of central stalk.
5 yellow petals.
Yellow avens flower.