Vines glabrous. Roots 10--20-fascicled. Stems simple or branched, to 1 m. Leaves (2 or)3- or 4-whorled; petiole 5--7 cm; leaf blade obovate or rarely oblong, 4--5 × 3--4 cm, veins 5--7, base narrowly cuneate, apex acute. Inflorescences axillary, sometimes basal ones in scale axils, 1-flowered; pedicel 1.5--2(--3) cm, basal 1/3(--1/2) adnate to leaf base. Perianth segments 4, erect, narrowly ovate to lanceolate, 1.2--1.5 × 0.4--0.6 cm, outer 2 segments narrower than inner ones. Stamens purple, shorter than perianth; filaments ca. 2 mm, basally connate; anthers 3--4 mm; appendage pale yellow, ca. 6 mm. Capsule ovoid. Seeds 4. Fl. Apr--Jul.

* Mountain slopes; 400--500 m. Shandong.