Arisaema costatum (Wall.) Mart.

Plants dioecious. Tuber brown outside, white inside, depressed globose, 3–5cm in diam. Cataphylls 3, ca. 50 × 25cm, membranous. Leaf solitary; petiole green, often slightly purplish, terete, 30–50cm, proximal 1/4–1/3 sheathing into pseudostem, ca. 1cm in diam.; leaf blade 3-foliolate; leaflets pale green abaxially, deep green adaxially, shortly petiolulate or subsessile; terminal elliptic or oblong, 16–30 × 9–16cm, base auriculate and rounded, inner base narrowly cuneate, apex acuminate; lateral veins very numerous and running almost parallel, distinctly raised abaxially, impressed adaxially. Peduncle emerging from pseudostem, shorter than petioles, 25–45cm. Spathe dark purple, with white longitudinal lines; tube cylindric, 4–8cm, slightly costate inside, but in Xizang specimens almost smooth inside, throat margins slightly recurved; limb incurved, narrowly ovate-oblong, 3–4cm, apex acuminate with a filiform tail. Spadix unisexual; female zone 2.4–3.5cm; ovary green; style short; stigma white, disciform; appendix pendulous from spathe, dark purple, very long flagelliform, 20–50cm, inflated toward base, base truncate, swollen disciform, with a stipe 3–5mm, smooth throughout; male zone 2–3.7cm; synandria of 3–5 stamens; connected filaments distinct; thecae dehiscing by a horseshoe-shaped slit.