Coarse biennial or perennial herb 1.2–3 m. tall; rootstock not seen.
Basal leaves to ± 65 × 40 cm., the lamina broadly deltoid-ovate, bi- to subtripinnatisect with (5–)6–7 pairs of pinnae, the lowest pinnae with petiolules up to ± 3 cm., but the lowest pinnulae sessile or very shortly stalked, pinnulae of lowest pinnae in 3–4 pairs; leaflets lanceolate-oblong, mostly at least twice as long as wide, ± 15–45 × 5–16 mm., dentate with rather blunt mucronate teeth, all but the lowest or lowest 2 pairs of leaflets decurrent along the axis and often confluent with the pair below, indumentum of short hairs along the margins and veins, longest and densest along the primary venation of the lower surface; petiole up to ± 25 cm. including the up to 10 cm., broad and tapering, striate, shortly hairy sheath, petiole and leaf-axis also pilose, especially between the pairs of pinnae; median stem leaves similar but smaller, bi- to subtripinnatisect becoming pinnate upwards, shortly petiolate to sessile with broad, clasping sheaths; upper leaves pinnate or sub-bipinnatisect, sessile, the very uppermost trisect or finally reduced to a very small lamina on the broad sheath.
Stem terete, widely fistular, striate, up to ± 1.5 cm. wide at the base, ± furnished with fine hairs; branches numerous above, opposite or whorled, divaricate.
Fruit oblong-elliptic (rarely obovate), distinctly emarginate at the base, emarginate or truncate above, margins not or feebly undulate, 7–11 × 4.5–8 mm., glabrous, fertile cell ± 2.5 mm. wide, slightly narrower than the wings, the basal sterile part below it 1–2.5(–3) mm. long; commissural vittae 2, long, clear, vallecular vittae solitary; stylopodia depressed-conical, the disk with a crenate border.
Ovary cylindrical-compressed, glabrous or hirtellous.
Inflorescence much-branched, initially with pairs or sometimes whorls of branches, branches with sessile or pedunculate terminal umbels below which 2 or more branches arise; umbels with ± 12–23 rays ± (2–)2.5–7 cm. long after petal fall, ± shortly pilose, sometimes obviously glabrous on the outer surface; involucre of 2–9 linear deciduous bracts ± 3–8 mm. long; partial umbels ± 13–26-flowered, pedicels 3–12 mm., indumentum similar to that of the rays; involucel of 4–8 bracteoles 2–6 mm. long; rays and pedicels often somewhat closed together below and spreading above in fruit; peduncles up to 8 cm. in the lateral umbels, shortly hairy.
Petals white or creamy, ± suffused with green centrally, obcordate, ± 1.5–2 mm., glabrous, univittate.