Arisaema wilsonii var. forrestii Engler.
Plants dioecious. Tuber dark brown outside, whitish inside, globose, 5-7 cm in diam., bearing some tubercles around. Cataphylls 3 or 4, dark purple, with tiny greenish stripes, to 30 × 7 cm, apex obtuse. Leaf 1(or 2); petiole to 130 cm, basal part sheathing into short pseudostem; leaf blade 3-foliolate; leaflets sessile, dull abaxially, light green adaxially, margins usually cristate or crenulate; midrib and lateral veins raised abaxially; central leaflet depressed obovate, 15-26 × 18-28 cm, base cordate, apex nearly truncate with a broad and short acumen; lateral leaflets rhombic or obliquely ovate, longer than central one, to 37 × 24 cm, apex abruptly acuminate. Peduncle yellowish green, shorter than petioles, ca. 35 cm, papillose. Spathe purple with yellowish stripes; tube cylindric, 6-8 × ca. 3 cm, throat margins slightly recurved; limb oblong or obovate-oblong, 10-15 × 5-8 cm, apex abruptly acute with an acuminate tail 3-4 cm, incurved. Spadix unisexual; female zone conic, ca. 2 × 1.3 cm; ovary green, obconic; style distinct; stigma purple; male zone 5.5-6 cm × 6-7 mm; synandria stipitate, lax; anthers 3 or 4, reniform, dehiscing by horseshoe-shaped slit. Appendix robust, greenish dark purple, to 23 cm in total, proximally narrowly pyramidal, ca. 1.4 cm in diam., base truncate with a stipe ca. 10 × 7-8 mm, distally gradually narrowed into flagellum, tortuous, sometimes pendulous. Berries red, oblong, ca. 10 × 7 mm when mature. Fl. May, fr. Jun.
● Broad-leaved forests, forest margins, grassy slopes; 1900-3200 m. Gansu, Sichuan (Emei Shan), SE Xizang, W Yunnan.
The long peduncle, which lifts the inflorescence as high as the leaf blade, is probably an adaptation to its grassy habitat and makes this species comparable to the Himalayan Arisaema propinquum Schott.