Plants annual, 40-90 cm tall. Stem erect, slender, branched in upper part of stem. Leaves alternate; petioles of lower leaves longer, gradually shorter in upper leaves; leaf blade ovate-oblong or ovate-lanceolate, 4-7 × 2-3 cm, often few ciliate basal glands, base cuneate, margin coarsely crenate, teeth mucronulate, apex caudate-acuminate. Inflorescences in upper leaf axils, 1-flowered; peduncles 3-4 cm. Pedicels bracteate above middle; bracts narrowly lanceolate. Flowers yellow or orange-yellow. Lateral sepals 2, subovate-orbicular, apex mucronulate. Lower sepal brown spotted, saccate, narrowed into a hooked spur; spur short, 2-lobed; tip acute. Upper petal suborbicular, ca. 1.5 cm in diam., apex rostellate, abaxial midvein broadly thickened, cristate; lateral united petals clawed, 2-lobed; basal lobes oblong, smaller, apex with a filamentous long hair; distal lobes dolabriform, large, 2.5-3 cm, apex acute. Anthers obtuse. Capsule elliptic. Fl. Aug-Sep.