Plants annual, 60-90 cm tall. Stem erect, branched. Leaves alternate; petiole 2-5 cm; leaf blade ovate or ovate-lanceolate, 8-15 × 3-7 cm, with few stipitate glands at basal margin, lateral veins 6-8 pairs, base cuneate, margin crenate-serrate, teeth mucronulate, apex caudate-acuminate. Inflorescences axillary, 1-flowered; peduncles short. Petioles bracteate above middle; bracts ovate. Flowers yellow, large, to 4 cm deep. Lateral sepals 2, broadly ovate-orbicular, margin coarsely dentate, rarely entire, apex acuminate, abaxial midvein narrowly carinate. Lower sepal saccate, constricted into an incurved spur; spur short, 2-lobed. Upper petal orbicular, abaxial midvein cristate; lateral united petals not clawed, 2-lobed; basal and distal lobes lanceolate, apex with a filamentous long hair; auricle inconspicuous. Filaments short; anthers obtuse. Ovary fusiform. Capsule linear. Seeds oblong or orbicular, ca. 3 mm. Fl. Jul-Aug, fr. Sep.
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