2n = 24. Accessory chromosomes are known to occur in some populations (Krishnappa, D.G. and M. S. Chennaveeraiah. 1974. Cytotaxonomy of Solanum indicum complex. Cytologia 40: 323-331; Chennaveeraiah, M. S, and D.G. Krishnappa.1965. The occurrence and behavior of accessory chromosomes in Solanum species. Nucleus 8: 161-170)
Solanum violaceum occurs across Asia, from India to China, Vietnam and Malaysia, from the coasts to inland mountains between ca. 3-27º latitude. It is commonly found in India, southern China, and Thailand. The westernmost recorded occurrence is the Indian Western Ghats. Chinese populations are restricted to the more southern regions of Fujian, Guangdong, Guangxi, Hainan, Hong Kong, Sichuan Taiwan, and Yunnan (Zhang et al. 1994). There are occasional collections from Sumatra and Java but it is not clear whether these are natural. It also occurs in Mauritius (Mauritius Island and Rodrigues Island) and on Reunion Island. Solanum violaceum does not seem to occur in the Philippines, New Guinea, or Australia. It is found in open places, abandoned cultivation, and roadsides from sea level to 2000 m elevation.
Solanum violaceum is a member of the Old World clade in subgenus Leptostemonum (Levin et al. 2006). Recent work suggests that S. violaceum is closely related to African endemic clades and is monophyletic, although the related S. multiflorum Roth ex Roem. & Schult. and S. hovei Dunal have not been sampled to date (Vorontsova et al. 2013)
Solanum violaceum is an small shrub with bright purple flowers, yellow to orange fruits held on erect pedicels, and prominent curved venation on its broadly lobed leaves. The leaf lobes are often an easy to recognise oblong shape. Inflorescences on herbarium specimens of S. violaceum dry stretched out with all peduncles straight and spread out flat to either side of the rachis, often almost at right angles to the rachis, whereas specimens of S. anguivi Lam. and S. multiflorum Roth dry with at least some peduncles curved and flowers and fruits overlapping. Fruit colour is recorded interchangeably as yellow or orange throughout the distribution range.
Unusually for a such a widespread Solanum species, Solanum violaceum is morphologically fairly uniform. The only region of high variability is Sri Lanka, with at least two morphotypes that may merit recognition as separate taxa. Populations with large dark purple corollas up to 3.2 cm in diameter and subentire leaves occur around 1200 m elevation and have long been noted in local floristic treatments (Hepper 1988; F.N. Hepper 4582, Badulla District, Sri Lanka). Plants with large, deeply lobed, strongly discolorous leaves and long straight prickles have been collected in Ramboda (A.H.G. Alston 448; Gardner s.n.). Outside Sri Lanka morphological outliers are not common, e.g. one collection with branched inflorescences and ca. 30 flowers per inflorescence (L.J.G. van der Maesen 2705, India), one collection with recurved pedicels and scarlet fruits like S. anguivi (J. Fernandes 1265, India), and one collection with leaves resembling S. aldabrense C.H.Wright (A.J.C. Grierson & D.G. Long 2675, Bhutan).
Solanum violaceum is sympatric with S. multiflorum in Tamil Nadu, India, S. hovei Dunal in the Indian Western Ghats, and S. deflexicarpum C.Y.Wu & S.C.Huang in Yunnan, China. Solanum multiflorum occurs at higher elevations and can be distinguished by its curved pedicels and stellate trichomes on the mature fruits; S. hovei is easy to separate from S. violaceum by its rhomboid leaves and sharply acute to acuminate leaf lobes; S. deflexicarpum often grows together with S. violaceum (S. Knapp, pers. comm.) and can be distinguished by its sharply curved pedicelsand smaller white flowers.
For the last 150 years the name “Solanum indicum L.” has been applied to both the Asian S. violaceum and the African S. anguivi Lam., as well as to other superficially similar taxa. Due to historic confusion and widespread misapplication, the epithet “indicum” was rejected (Hepper 1978). Richard Lester’s group (Roberts 1978, Niakan 1980, Lester and Durrands 1984, Lester and Niakan 1986) used protein electrophoresis, seed surface enzyme digests and crossing studies to show that S. violaceum is distinct from S. anguivi. The distributions of S. violaceum and S. anguivi do not overlap; the closest proximity of the two species is S. violaceum in Mauritius and S. anguivi in Madagascar. The two species often look alike on superficial examination but the differences soon become obvious. Solanum violaceum can be distinguished from S. anguivi by its mauve to purple corolla 1.3-3 cm diameter (versus usually white corolla 0.8-1.5 cm diameter in S. anguivi), anthers 4.5-8.5 mm long (versus anthers 3.5-5 mm long in S. anguivi), fruiting pedicels 1.2-1.8 mm long (versus fruiting pedicels 0.8-1.3 mm long in S. anguivi), petiole 1/5-3/5 of the leaf length (versus petiole 1/4-1/6 of the leaf length in S. anguivi), leaves with frequent secondary lobing (versus almost no secondary lobing in S. anguivi), and glaucous abaxial leaf surface with prominent venation curving outwards (versus usually green-brown abaxial surface with less pronounced, more or less straight venation in S. anguivi). Solanum violaceum was neotypified by Knapp (2013).
Solanum kurzii was recognised as a species by Mill (2001) but represents an unarmed version of S. violaceum, a character that varies between growth conditions. Wilhelm Kurz, curator of the Calcutta herbarium, annotated a Calcutta specimen from the Watt herbarium “Solanum pubescens.” Clarke (1883) named it “S. pubescens var. ? lobatum”, to distinguish it from the entire-leaved S. pubescens Willd. Brace thought that this entity was distinct from S. pubescens and suggested the name Solanum kurzii in an unpublished manuscript; the name was later effectively published by Prain (1896). The collection G. King s.n. [K000441390] would be a suitable lectotype for Solanum kurzii Brace ex Prain, as it is a specimen cited by both Brace and Prain.
Solanum junghuhnii Miq from Java resembles S. violaceum but has condensed inflorescences and rhomboid leaves; further study is needed to establish whether they are conspecific.This name is considered a synonym of S. violaceum pending further in-depth study of the Asian spiny solanums.
Clarke, C.B. 1883. Solanum. In: J.D. Hooker (ed.) Flora of British India 4: 229-237.
Hepper, F.N. 1978. Typification and name changes of some Old World Solanum species. Bot. J. Linn. Soc. 76: 287-292.
Hepper, F.N. 1988. Solanaceae. In: M.D. Dassanayake (ed.), A revised handbook to the flora of Ceylon 6: 365-409.
Jarvis, C.E. 2007. Order out of chaos: Linnaean plant names and their types. London: Linnean Society of London in association with the Natural History Museum.
Lester, R.N. & P. Durrands. 1984. Enzyme treatment as an aid in the study of seed surface structures of Solanum. Ann. Bot. (Oxford) 53: 129-131.
Knapp, S. 2013. Typification of Solanum (Solanaceae) described by Casimiro Gómez Ortega. Anales del Jardín Botánico de Madrid 70: 56-61.
Lester, R.N. & L. Niakan. 1986. Origin and domestication of the Scarlet Eggplant, Solanum aethiopicum, from S. anguivi in Africa. In: W.G. D’Arcy (Ed.), Solanaceae: Biology and Systematics, pp. 433-456. Columbia University Press, New York.
Levin, R.A., N.R. Myers, & L. Bohs 2006. Phylogenetic relationships among the "spiny" solanums (Solanum subgenus Leptostemonum). Amer. J. Bot. 93: 157-169.
Mill, R.R. 2001. Solanaceae. In: Flora of Bhutan 2(3): 1037-1078.
Niakan, L. 1980. Biosystematics of the Scarlett Eggplant (Solanum aethiopicum L.) and related species. PhD Dissertation, University of Birmingham.
Prain, D. 1896. Noviciae Indicae XIV. Some additional Solanaceae. J. Asiat. Soc. Bengal, Pt. 2, Nat. Hist. 65: 541-543.
Roberts, P.A. 1978. Interrelations of Globodera and some Solanum (Leptostemonum) species. PhD Dissertation, University of Birmingham.
Zhang, Z.Y., A.M. Lu and W.G. D’Arcy. 1994. Solanaceae. In: Z.Y. Wu and P.H. Raven (eds.), Flora of China 17: 300-332. Science Press (Beijing) and Missouri Botanical Garden (St. Louis).
Vernacular names. Sri Lanka - tita-batu (F.N.Hepper 4518, 4599); Thailand - mawêng ton (A.F.G. Kerr 9048).
Uses. Fruits small and bitter, not used by people (F.N.Hepper 4518); bitter all purpose medicine (F.N.Hepper 4599); used to treat blood diseases (N.G.Patel s.n., 1983). The root is very bitter and the juice is applied to the nipples by bad women to prevent the infant from taking the breast; the root in the form of a decoction made with boiling water used as a remedy for gonorrhoea by the Gomor (Anon. s.n., Malaysia, 1914). Fruit used in the treatment of diabetes “by Dr. Yai Sanitwongse” (A.F.G. Kerr 9048).