Description from Flora of China
Shrubs erect, many branched, to 0.7 m tall, most parts densely stellate tomentose. Stipules subulate; petiole 2-4 cm, stellate tomentose; leaf blade obovate, oblong, or suborbicular, 5-20 × 3-10 mm, abaxially stellate tomentose, adaxially sparsely stellate hairy or subglabrous. Flower solitary, axillary. Pedicel ca. 1 cm, stellate tomentose, articulate at middle. Calyx campanulate, ca. 6 mm in diam., abaxially densely stellate tomentose, lobes triangular, ca. 2.5 mm. Corolla yellow, ca. 1.2 cm in diam.; petals obovate, ca. 6 mm. Filament tube ca. 4 mm, hirsute, filaments slender; anthers yellow. Schizocarp globose, ca. 4 mm in diam., upper surface broadly conical with prominent radial grooves; mericarps 7 or 8, enclosed by persistent calyx, smooth, pilose apically, apex not awned. Fl. winter-spring.
Some material named as Sida chinensis looks much like a hairy form of S. acuta with very acute but awnless sculptured mericarps.
● Sunny slopes, streamsides. Hainan, Taiwan, Yunnan.