Erect, annual, glabrous, usually profusely branching herb, up to 1.3 m tall with a well-developed taproot. Stem solid, subterete, up to 2 cm in diameter; older internodes sometimes becoming hollow, sulcate, mostly with a white bloom, light green with darker green ribs, occasionally violet. Leaves alternate, rather variable in shape, size and number, with a yellow-green, scariously margined sheath surrounding the supporting stem for up to three-quarters of its circumference; petiole and rachis subterete, sulcate, light green; blade white waxy, shiny green often with darker green veins; basal 1-3 leaves usually simple, withering early, often in a rosette, blade ovate in outline, deeply cleft or parted into usually 3 incised-dentate lobes; next leaves decompound, petiole 0-15 cm long, blade ovate or elliptical in outline, up to 30 cm x 15 cm, usually pinnately divided into 3-11 leaflets, each like the blade of the simple lower leaves or again pinnately divided into 3-7 simple leaf-like lobes; all higher leaves compound, petiole restricted to the sheath, blade divided into 3 leaflets of which the central one is largest, each often variously divided into ultimately sublinear, entire, acute lobes. Inflorescence an indeterminate, compound umbel; peduncle up to 15 cm long; bracts sublinear, 0-2, up to 11 mm long; primary rays 2-8, up to 4.5 cm long; bracteoles 0-6, linear, up to 1 cm long; secondary rays up to 20, up to 5 mm long; usually each umbellet has bisexual peripheral flowers, and the central flowers are sometimes male; calyx in all flowers represented by 5 small lobes; corolla with 5 white or pale pink petals, heart-shaped, very small (1 mm x 1 mm) in male flowers, in bisexual peripheral flowers usually 3 petals are larger: 1 petal develops 2 ovate lobes of about 3 mm x 2 mm and the 2 adjacent petals each develop one lobe; stamens 5, filaments up to 2.5 mm long, white; pistil rudimentary in male flowers, in bisexual flowers with inferior ovary, a conical stylopodium bearing 2 diverging styles up to 2 mm long, each one ending in a minutely papillate stigma. Fruit an ovoid to globose schizocarp, up to 5 mm in diameter, yellow-brown with 10 straight longitudinal ribs alternating with 10 wavy longitudinal ridges, often crowned by the dry persistent calyx lobes and the stylopodium with styles; fruit does usually not split at maturity; it contains 2 mericarps which each bear on their concave side 2 longitudinal, rather wide lines (vittae), containing essential oil. Seed 1 per mericarp, with testa attached to the fruit wall. Seedling with epigeal germination; taproot thin with many lateral roots; hypocotyl up to 2.5 cm long; cotyledons opposite, oblanceolate, up to 3 cm x 4 mm, pale green.