Very robust herb with watery sap, up to ± 2 m. tall; stem branched, grooved, up to ± 10 cm. diam. at base; stock very stout, taproot very deeply descending; offset plants arising from short stout rhizomes. Petioles (15)-20-30(40) cm. × (5)-10-20 mm., concave with stout median rib on ventral, convex on dorsal surface; sheath broad, tapering to petiole, with short broad rounded to toothed ligule, or ligule obsolete. Lamina about oblong to ovate-oblong in outline, 2-pinnate or sts ± 3-pinnate, (1)-2-4(6) dm. × (5)-15-20-(25) cm., coriac., light to rather dark green; veins evident on both surfaces. Primary pinnae, 5-10-(15) pairs, distant, broad ovate-oblong in outline, (5)-15-(20) × (3)-4-10 cm., with short slightly sheathing petiolule. Secondary pinnae 3-5 pairs, obliquely ovate-oblong, up to 5-(10) × 1-3 cm., sessile by very broad base, unequally 3-5 lobed; lobes about ovate-oblong, with cartilaginous margins produced into pungent points 2-3 mm. long. Stem-bracts with open concavo-convex sheaths up to 10 × 6 cm., narrowed to lamina up to c. 6 cm. long. Umbels compound, ± 4-8 cm. diam., us many ± aggregated into heads up to c. 2 dm. diam. Primary rays many, stout, unequal, up to ± 3 cm. long; involucral bracts linear, acute, pungent, 3-5 cm. × 5-10 mm. Secondary rays and bracts similar, shorter. Fls ∞; calyx-lobes unequal, narrowly ovate-triangular, subacute; petals broad-ovate, abruptly acute; ♂ with pistillodes bearing minute styles, ♀ with conical stylopodia and long styles. Fr. 4-5 mm. long; mericarps unequal, with 5-(4-3) ridges; vittae long, 1 per furrow.

2n = 22