Plants annual, 40-50 cm tall, with few supporting roots, glabrous. Stem erect; branchlets spreading, slender. Leaves alternate; petiole 5-12 mm, without glands; leaf blade pale green abaxially, dark green adaxially, oblong or ovate-oblong, 10-15(-20) × 3-6 cm, submembranous, not setose between teeth, lateral veins 6 or 7 pairs, curved, prominent abaxially, margin crenate, teeth mucronulate, apex acuminate or caudate-acuminate. Inflorescences in upper leaf axils or terminal of branchlets, racemose, 6-8-flowered; peduncles suberect, shorter than leaves, 6-7 cm. Pedicels spreading, 1-1.5 cm, elongate at fruiting, bracteate at base; bracts persistent, subulate, 2-3 mm, apex acute. Flowers yellow, ca. 4 cm deep. Lateral sepals 2, reniform-orbicular, ca. 5 × 3-4 mm, tortuous, membranous, apex cuspidate. Lower sepal saccate, to 2 cm deep, abruptly narrowed into an incurved spur; spur ca. 1.5 cm, stout; mouth oblique, 1-1.5 cm wide, tip acute. Upper petal reniform, ca. 1.5 cm, apex rostellate, abaxial midvein thickened, carinate; lateral united petals broadly clawed, 2-2.5 cm, 2-lobed; basal lobes orbicular, small; distal lobes dolabriform, longer, apex rounded; auricle inflexed, purple spotted. Filaments short, broad; anthers ovoid, apex acute. Ovary erect, fusiform. Capsule linear, 4-5 cm. Seeds many, brown, oblong-obovoid, ca. 4 mm. Fl. Aug-Sep.
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