Plants annual, 20-60 cm tall, subglabrous, with few supporting roots. Stem erect or laxly branched, soft, slender or stout basally; branches slightly curved. Leaves alternate, petiolate, subsessile in upper ones; petiole 1-4 cm, slender; leaf blade ovate, oblong, or subelliptic, or upper ones ovate-lanceolate or oblong, 4-8.5 cm, thinly membranous, lateral veins 4-6 pairs, fine, base broadly cuneate or subrounded, upper ones rounded or cordate, margin coarsely crenate, teeth mucronulate, apex obtusely caudate. Inflorescences in leaf axils, 1-3-flowered; peduncles fibrous, 1-3 cm, sparsely puberulent or glabrous. Pedicels 1-1.5 cm, elongate at fruiting, bracteate at middle; bracts persistent, linear-setose, ca. 2 mm. Flowers pink, small, ca. 1.5 cm deep. Lateral sepals 2, ovate, 3-4 mm, abaxial midvein obtusely cristate, base cordate, margin entire or denticulate on one side, apex acute or acuminate. Lower sepal navicular, vertical, with a curved spur; spur subequal to limb, 5-6 mm, apex with a groove or 2-fid. Upper petal orbicular, 6-8 mm in diam., cucullate, abaxial midvein narrowly cristate at middle; lateral united petals not clawed, 1.2-1.4 cm, 2-lobed; basal lobes small, sometimes rudimentary; distal lobes reflexed, clawed, lunar, abruptly narrowed basally, apex obtuse; auricle conspicuous, dentate or rounded. Filaments slender; anthers small, obtuse. Ovary erect, fusiform. Capsule linear, 2.5-3.5 cm, torulose. Seeds many, brown, elliptic, 3.5-4 mm, shiny. Fl. Aug.