Plants annual, 50-100 cm tall. Stem usually slender, glabrous, branched. Leaves alternate, lower leaves long petiolate, upper leaves sessile; petiole 2-5.5 cm, with stipitate or sessile basal glands; leaf blade elliptic-ovate, elliptic, or oblong-lanceolate, 8-20 × 2.5-5.5(-6) cm, membranous, both surfaces glabrous, setose between teeth, lateral veins 9-12 pairs, base cuneate, margin crenate, apex caudate-acuminate. Inflorescences usually axillary or subterminal, 3-5-flowered; peduncles spreading or ± curved, shorter than or longer than leaves, slender. Pedicels longer than bracts, fibrous or slender; bracts persistent, ovate-lanceolate. Flowers yellow or pale purple, red striate, ca. 2.5 cm in diam. Lateral sepals 2, obliquely ovate, often with glands on one side. Lower sepal obliquely saccate, short, abruptly narrowed into an incurved or hooked, short spur. Upper petal orbicular, abaxial midvein inconspicuously carinate; lateral united petals not clawed, 2-lobed; basal lobes orbicular; distal lobes dolabriform, apex acute; auricle inflexed, small. Anthers obtuse. Capsule linear, ca. 2.5 cm. Seeds brown, oblong, smooth. Fl. Jun-Aug. 2n = 18, 36.
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