Description from Flora of China
Trionum annuum Medikus.
Herbs annual, erect or procumbent, 25-70 cm tall; stems slender, white stellate hirsute. Stipules filiform, ca. 7 mm, stellate coarsely hirsute; petiole 2-4 cm, stellate hirsute and stellate puberulent; leaf blade 3-6 cm in diam., dimorphic; blades on proximal part of stem orbicular, those on distal part of stem palmately 3-5-lobed, central lobe longer, lateral lobes shorter, lobes obovate to oblong, usually pinnate, sparsely stellate spiny hairy abaxially, sparsely hirsute or glabrous adaxially. Flowers solitary, axillary. Pedicel ca. 2.5 cm, elongated to 4 cm in fruiting, stellate hirsute. Epicalyx lobes 12, filiform, connate at base, ca. 8 mm, hirsute. Calyx greenish, campanulate, swollen, connate for ca. 1/2 length, 1.5-2 cm, membranous, long hirsute or stellate hirsute, lobes 5, triangular, longitudinally purple-veined. Corolla very pale yellow with purple center, 2-3 cm in diam.; petals 5, obovate, ca. 2 cm, abaxially sparsely very minutely puberulent. Staminal column ca. 5 mm; filaments slender, free for ca. 3 mm; anthers yellow. Styles 5, glabrous. Capsule oblong-globose, ca. 1 cm in diam., coarsely hirsute; mericarps 5, endocarp black, thin, exocarp papery. Seeds black, reniform, glandularly verrucose. Fl. Jul-Oct.
Ruderal weed. Throughout China [Kazakhstan, Kyrgyzstan, Mongolia, Tajikistan, Turkmenistan, Uzbekistan; pantropical].