Description from Flora of China
Lettsomia sumatrana Miquel, Fl. Ned. Ind., Suppl. 560. 1860; Ipomoea rotundisepala Hayata; I. staphylina Roemer & Schultes var. malayana Prain.
Climbers woody, with glabrous, sometimes verruculose axial parts. Stems twining or prostrate, to 20 m. Petiole 4.5-10 cm, scabrous; leaf blade broadly ovate, (3.5-)8-16 X (4-)7-13 cm, ± leathery, abaxially often pubescent, adaxially subglabrous, base shallowly cordate to truncate, margin entire, apex obtuse, acute, or short acuminate; lateral veins usually 11-14 pairs, prominent abaxially. Inflorescences paniculate, fundamentally cymose, 10-15 cm; peduncle 3-13 cm; basal bracts leafy; bracteoles early deciduous, ovate, 1-1.5 mm. Pedicel 7-10 mm. Sepals slightly unequal, glabrous; outer 2 broadly ovate, 3.5-5 mm, apex obtuse; inner 3 ± circular, 4.5-6 mm, apex broadly rounded or emarginate. Corolla lilac or greenish white, with a reddish purple tube inside, tubular-funnelform, 3-3.5 cm, glabrous. Stamens included, unequal; filaments inserted ca. 1.5 mm above base of corolla. Ovary conical, glabrous. Stigma 2-lobed. Capsule ovoid, 8-9 mm, apex ± acute. Seeds black-brown, ca. 4 mm, hilum with a tuft of long sericeous hairs.
Ipomoea sumatrana was treated in Fl. Reipubl. Popularis Sin. as I. staphylina Roemer & Schultes. The latter is a very closely related Indian species. Ooststroom (l.c. 572) recognized both species and separated I. sumatrana by having thicker leaf blades with 11-14 pairs of lateral veins, tubular-funnelform corollas 3-3.5 cm, and filaments inserted ca. 1.5 mm above corolla base, and I. staphylina by having thinner leaf blades with 7-8(-11) pairs of lateral veins, broadly funnelform to campanulate corollas ca. 2 cm, and filaments inserted ca. 2.5 mm above corolla base. The Chinese material agree much more closely with I. sumatrana. It is possible that I. staphylina occurs in SW China, but no specimens have been seen in herbaria outside of China.
Thickets, roadsides, forest margins; 100-900 m. SE Guangxi, Hainan, Taiwan, S Yunnan [Indonesia, Laos, Malaysia, ?Myanmar, Thailand]