Plants annual, 30-60 cm tall. Stem erect, yellow-brown puberulent in upper part when young, hairs ± deciduous later, subglabrous, long naked in lower part, nodes turgid, sulcate when dry, glabrous, laxly branched. Leaves alternate; petiole 1-2.5 cm; leaf blade gray-green abaxially, dark green adaxially, ovate or ovate-lanceolate, (6-)7-11 × 2.5-4.5 cm, papery, abaxial midvein sparsely pilose or glabrate, adaxially strigose, lateral veins 5-7 pairs, curved, base broadly cuneate, attenuate into petiole, margin crenate-serrate, teeth glandular-mucronulate, apex long acuminate. Inflorescences in leaf axils in upper part of stem and branches, 3-5-flowered; peduncles erect or ascending, shorter than leaves, 3-5 cm. Pedicels 1-2 cm, bracteate at base; bracts persistent, green, broadly ovate, ca. 3 mm, thick, apex cuspidate. Flowers yellowish, purplish striate, 2.5-3 cm deep. Lateral sepals 2, orbicular, 0.8-1 cm in diam., membranous, reticulate veined, apex glandular mucronulate. Lower sepal broadly saccate, ca. 2 cm deep, abruptly constricted into an incurved spur 4-5 mm; mouth oblique, ca. 1.4 cm, tip acute. Upper petal suborbicular, ca. 1.5 cm in diam., abaxial midvein thickened, with horn-shaped crista at middle; lateral united petals not clawed, ca. 2.5 cm, 2-lobed; basal lobes suborbicular, ca. 1 cm wide; distal lobes broadly ovate, longer, apex obtuse. Filaments linear, 4-5 mm; anthers acute. Ovary linear. Capsule not seen. Fl. Jul-Aug.
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