Description from Flora of China
Malvastrum carpinifolium (Linnaeus f.) A. Gray; Sida acuta subsp. carpinifolia (Linnaeus f.) Borssum Waalkes; S. acuta var. carpinifolia (Linnaeus f.) K. Schumann; S. acuta var. intermedia S. Y. Hu; ?S. bodinieri Gandoger; S. carpinifolia Linnaeus f.; S. carpinifolia var. acuta (N. L. Burman) Kurz; ?S. chanetii Gandoger; S. lanceolata Retzius; S. scoparia Loureiro; S. stauntoniana Candolle.
Subshrubs or herbs erect, 1-2 m tall. Branchlets pilose or subglabrous. Leaves ± distichous; stipules filiform, 4-6 mm, often longer than petiole, usually persistent; petiole 4-6 mm, sparsely pilose; leaf blade ovate, oblong, lanceolate, or linear-lanceolate, 2-5 × 0.4-1 cm, both surfaces glabrous or sparsely stellate pilose, rarely with simple hairs adaxially, base obtuse, margin dentate, sometimes partly entire toward its base, apex acute or acuminate. Flowers solitary or paired, axillary, sometimes congested at stem apex. Pedicel 4-12 mm, pilose, articulate at middle. Calyx shallowly cup-shaped, connate in basal 1/2, ca. 6 mm, mostly glabrous, margins often ciliate, lobes 5, caudate. Corolla yellow, less often white or yellow-orange, 8-10 mm in diam.; petals obovate, 6-7 mm, ciliate, base attenuate, apex rounded. Filament tube ca. 4 mm, sparsely hirsute. Schizocarp nearly globose; mericarps (4-)6(-9), segmentiform-tetrahedral, ca. 3.5 mm, basally transversely ridged, side walls reticulate-veined, glabrous, apex beaked, ± extending into 2 awns, apically dehiscent. Seed trigonous, ca. 2 mm, glabrous except around hilum. Fl. winter-spring.
The glabrous calyx is usually diagnostic for Sida acuta. Sida bodinieri was described as glabrous and if correctly placed in Sida would most likely belong under S. acuta. Sida chanetii was related by the original author to S. acuta but it was based on a collection from near Beijing, well north of any other records for Sida, and so its identity needs confirmation.
The bark is a good fiber source, and the roots are used medicinally.
Scrub, roadsides, wastelands. Fujian, Guangdong, Guangxi, Hainan, Taiwan, Yunnan [Bhutan, Cambodia, India, Laos, Nepal, Thailand, Vietnam].