There is a vast literature on the genus Sida. Many more local treatments are available, especially for Central and South American regions.
Sida is a relatively large genus of ca. 250 species from tropical and subtropical areas in America, Africa, Asia and Australia. Several species are noxious agricultural weeds, some are cultivated as ornamentals.
Given their tropical origin, species of Sida are often reluctant to flower in Belgium. The two species treated here have been recorded in flower and fruit and there is no doubt about there identity. Additional species possibly occur. A rather typical plant with slightly rhomboid to ovate leaves has been recorded in 2005 in the port of Gent near a soybean mill. It possibly belongs to Sida ovata Forssk. (comm. P.A. Fryxell) or, less likely, to S. alnifolia L. A similar species, Sida cordifolia L., was recently found as a weed in a lily field in the Netherlands (Holverda & al. 2009, Reijerse & Verrijdt 2010).
- Mericarps 8-14. Leaves rhomboid, cuneate at base. Pedicels 10-30 mm long, much longer than the subtending petiole. Lowest stipules never transformed to hard spines === 1. Sida rhombifolia
- Mericarps 5. Leaves ovate, cordate at base. Pedicels 2-10 mm long, shorter or at most as long as the subtending petiole. Lowest stipules transformed to hard spines, 0,5-1,5 mm long === 2. S. spinosa
Literature
Brandao J.L., Baracho G.S., Ferreira de Sales M., Viegas Filho M.P. (2017) Synopsis of Sida (Malvaceae, Malvoideae, Malveae) in the state of Pernambuco, Brazil. Phytotaxa 307(3): 205-227.
Clement I.D. (1957) Studies in Sida. Contr. Gray Herb. 180: 1-91.
Fryxell P.A. (1985) Sidus sidarum – V. The North and Central American species of Sida. Sida 11(1): 62-91.
Fryxell P.A. & Hill S.R. (2015) Sida. In: Flora of North America Editorial Committee (eds.), Flora of North America North of Mexico, vol. 6. Oxford University Press, New York: 310-319. [available online at: http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=130307]
Holverda W., van Moorsel R. & Duistermaat L. (2009) Nieuwe vondsten van zeldzame planten in 2005, 2006 en ten dele 2007. Gorteria 34: 1-40.
Kearny T.H. (1958) A tentative key to the South American species of Sida L. Leafl. W. Bot. 8: 249-270.
Reijerse F. & Verrijdt T. (2010) Sida spinosa L., S. rhombifolia L., S. cordifolia L. en Malvastrum coromandelianum (L.) Garcke adventief op lelievelden. Gorteria 34: 121-136.
Tambde G.M., Gore R.D. & Sardesai M.M. (2016) A Synopsis of the genus Sida L. (Malvaceae) from Maharashtra, India. Taiwania 61(3): 243-252. [available online at: http://tai2.ntu.edu.tw/taiwania/pdf/tai.2016.61.243.pdf]
Viarouge N., Marnotte P. & Merlier H. (1995) Détermination pratique des mauvaises herbes du genre Sida L. Agriculture et développement 8: 43-50.