Seedling
Hypocotyls are green or tinged with maroon, smooth and fragile. Cotyledons are narrowly elliptic, about 12-15 mm long, dull green on the upper surface with maroon on the underside, becoming green with age. Young leaves have a gray-mealy coating, especially on the leaf undersides and the emerging leaves. The first pair of leaves are opposite; all others alternate. Margins of very young leaves are entire or have a few teeth. Stems of young seedlings are covered with mealy-white granules.
Juvenile plant
Stems are erect, branching, hairless, vertically ridged, often with maroon stripes. Leaves are petiolated, rhombic to egg-shaped to lanceloate, alternate, 3-10 cm long, and irregularly toothed. Some blades have a white-mealy coating, but this is restricted to younger leaves. Lower leaves are 2.5-7.5 cm long, almost always irregularly toothed.
Mature plant
As lamb's-quarters plants mature, the upper leaves are sometimes linear, lack petioles, and may have entire leaf margins.
Root structure description
Common lambsquarters plants have short and branched taproots.
Flowers
Flowers are produced from June to September on spikes grouped into a panicle arising from the ends of stems and the leaf axils. Individual flowers are inconspicuous, sessile, small, green, and aggregated into dense small clusters. The fruit is a utricle with a papery thin covering over a single seed. A single plant can produce thousands of seeds.
Post senescene
Erect woody stems and seedheads persist through the winter. Dead stems and remnants of the inflorescence are often red to purple.
