Description from Flora of China
Herbs perennial or annual, subshrubs or shrubs, to 2 m, most parts with stellate, simple and/or glandular hairs. Leaves simple; stipules threadlike to narrowly lanceolate; leaf blade entire (sometimes lobed), margin usually dentate, without foliar nectaries. Flowers solitary or paired, axillary or subterminal, often in axillary or terminal racemes or panicles, rarely in umbels or glomerules. Epicalyx absent. Calyx campanulate or cup-shaped, 5-lobed, often 10-ribbed basally and plicate in bud. Corolla mostly yellow, rarely white or ± orange [or rose or purplish], sometimes with a dark center. Petals 5, free, basally connate. Filament tube pubescent or glabrous, with many anthers at apex. Ovary 5-10-loculed; ovules 1 per locule, pendulous; style branches as many as carpels; stigma capitate. Schizocarp ± disk-shaped or globose; mericarps (4-)5-10(-14), sculptured or smooth, sometimes partly membranous, mostly beaked, often with 1 or 2 apical awns, often minutely stellate puberulent, dehiscent or indehiscent. Seeds 1 per mericarp, smooth, glabrous except sometimes for minute hairs around hilum.
Many species of this genus are used as fiber sources. Some species are widespread ruderals with sporadic distributions. Material with fully mature fruits is needed for reliable determinations. Studies of African material have demonstrated that there are superficially similar species that differ most obviously in details of mericarp morphology, and detailed studies have led to the recognition of more, rather than fewer, taxa. More information is needed on variation within populations, particularly in mericarp morphology, to assess the status of the awnless species of Sida, as there are indications that awned and awnless mericarps can occur on the same plant, thereby suggesting a possible reduction in species numbers.
Sida cavaleriei H. Léveillé is a synonym of Alectra arvensis (Bentham) Merrill in the Scrophulariaceae (see Fl. China 18: 86. 1998).
Between 100 to 150 species: Africa, Asia, Australia, North and South America, Pacific islands; ca. 2/3 of the species American; 14 species (six endemic) in China.