Annual herb 0.5-6 dm. tall, alternately branched above; leaves oblong-ovate, the blade 3.5-10 cm. long, 3.5-8 cm. broad, 3-4-pinnately decompound, the ultimate divisions filiform, 1.5-7 mm. long, the petiole 2.5-11 cm. long; umbels compound or some simple, pedunculate or sessile, the peduncles to 2 cm- long; involucre and involucel lacking; rays 3-5, 1-2.2 cm. long, the pedicels 2-8 mm. long; carpophore shortly 2-cleft; fruit ovoid, 1.2-3 mm. long, 1.5-2 mm. broad.
Petals very small, ± 0.3–0.5 mm., white, glabrous.
Fruit almost round, laterally compressed, 1.25–1.75 mm., with strongly protuberant, broad, pale primary ribs, sometimes purplish tinged, the valleculae very narrow at maturity, central fruit frequently sessile; stylopodia very small, styles extremely short or absent.
Umbels 2–4-rayed, sessile (sometimes apparently pedunculate through branch reduction), rays 9–15 mm., involucre absent; flowers 5–16 in each partial umbel, pedicels (0–)1.5–7 mm., involucel absent.
Weak, glabrous annual with a slender taproot, erect or sprawling, simple or with several stems from the base, the stems strongly striate, often branched chiefly below the middle with long, ascending branches, 15–60 cm.
Lower and central stem leaves ± ovate in outline, tripinnate with filiform, 3–18 × 0.25–0.7 mm., shortly mucronate segments; sheaths 3–15 mm., strongly nerved centrally with broad membranous margins; petioles slender, 0.8–5 cm.; basal leaves often withering in ripe fruit, with usually shorter but still very narrow segments; upper leaves ± sessile, with few very long segments up to 3 cm. long.
Umbels often subsessile and appearing superficially like a group of simple umbels, mostly lateral in the axils of leaves, but when present the peduncles may reach 2 cm. long. Rays 2–5, 7–15 mm. long; bracts and bracteoles 0; partial umbels with 5–15 flowers on fine, rather irregular pedicels 2–6 mm. long.
Calyx teeth minute; petals white.
Low, weak, glabrous annual herbs up to 50 cm., sometimes branched from the base with a number of stems of equal magnitude, sometimes branched above with a distinct main stem, often semi-decumbent.
Fruit broadly elliptic to nearly round, quite strongly laterally compressed; stylopodium small, shortly conical; styles minute with almost sessile stigmatic surfaces. Ribs strongly developed and rather obtuse, with only narrow intervals between them at maturity.
Stem terete, with relatively coarse grooving.
Carpophore very slightly 2-cleft at the apex; seed subterete to pentagonal in section; vittae minute.