Plants annual, 50-100 cm tall, with many supporting roots, glabrous. Stem erect, robust, naked in lower part, branched in upper part; branches sulcate when dry. Leaves alternate, appearing subverticillate, often crowded at upper parts of stem and branches, petiolate, uppermost leaves sessile or subsessile; petiole absent or 6-7 cm; leaf blade gray-green abaxially, dark green adaxially, ovate-lanceolate, rarely ovate-elliptic, (8-)10-16 × 3.5-7 cm, rigid, often with 1 pair of sessile globose basal glands, setose between teeth, lateral veins (7 or)8-10 pairs, curved, midvein conspicuous, base broadly cuneate, gradually attenuate into petiole, margin densely coarsely crenate, apex acuminate or caudate-acuminate. Inflorescences terminal or axillary, racemose, 8-13(-16)-flowered; peduncles overtopping or ca. as long as leaves, 8-16(-20) cm. Pedicels 1.5-2 cm, bracteate at base; bracts caducous, broadly ovate or ovate-lanceolate, 3-4 mm, membranous, apex scarcely mucronulate or cuspidate. Flowers yellow, upper petal and lateral united petals pink-purple spotted, 2-2.5 cm deep. Lateral sepals 2, yellow-green, obliquely orbicular or suborbicular, 7-8 mm in diam., ± leathery, many veined, midvein absent, apex hardly mucronulate. Lower sepal saccate, 2-2.5 cm, gradually narrowed into an incurved spur 1.5-1.8 cm; mouth subvertical, 8-10 mm wide, tip mucronulate. Upper petal deeply saccate, suborbicular, 8-10 mm in diam., abaxially rounded carinate, apex obtuse; lateral united petals not clawed, base broadly cuneate, 2-2.5 cm, 2-lobed; basal lobes orbicular, small; distal lobes dolabriform, ca. 2 × as large as basal lobes, apex obtuse-rounded; auricle narrow. Filaments short, ca. 4 mm; anthers ovoid, apex obtuse. Ovary fusiform. Capsule linear, 3-3.5 cm. Seeds many, brown, obovoid-oblong, ca. 4 mm, tuberculate. Fl. Aug-Sep.
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