Solanum candidum
2n=24 (Whalen et al. 1981)
A low to middle elevation species encountered from sea level to about 1500 m, occurring naturally in open woodlands and thickets and in light gaps near watercourses in quebradas and barrancas; in partial shade or open sun; versatile in soil tolerance, on both limestone and granite derived soils of diverse textures; in seasonally dry to relatively wet situations; commonly occuring as a successional species in human clearings and disturbances. Extending from barranca woodlands and oak forests of southern Sonora and Chihuahua in Mexico south along the Sierra Madre Occidental to central Mexico, widespread and common in Southern Mexico, Guatemala and El Salvador, apparently less abundant in the remainder of Central America, also in the Chocó of Colombia and lowlands of Ecuador and northern Peru.
Solanum candidum belongs to the Leptostemonum clade of Solanum (Bohs, 2005). Within Leptostemonum, it belongs to the Lasiocarpa clade, a monophyletic group that includes most of the species traditionally recognized in Solanum section Lasiocarpa Dunal (Whalen et al., 1981; the S. quitoense species group of Whalen, 1984; Levin et al., in press). Within this clade, chloroplast sequences from the trnT-F region indicate that S. candidum belongs to a clade that also includes S. felinum, S. hyporhodium, S. lasiocarpum, S. pseudolulo, S. quitoense, S. repandum, and S. vestissimum (Bohs, 2004). Resolution is poor to non-existent among the species of this latter clade. Nuclear waxy sequence data indicate that S. candidum is most closely related to the Asian species S. repandum and S. lasiocarpum (L. Bohs, unpubl.data). This result is consistent with the hypothesis of Heiser (1986, 1987, 1996) that S. candidum may be one of the closest relatives of the disjunct Asian species of Solanum section Lasiocarpa.
Whalen, M.D., D.E. Costich & C.B. Heiser, Jr. 1981. Taxonomy of Solanum section Lasiocarpa.
Gentes Herb. 12: 41-129.
Whalen, M.D. 1984. Conspectus of species groups in Solanum subgenus Leptostemonum.
Gentes Herbarum 12 (4): 179-282.
Heiser, C.B., Jr. 1986. A new domesticated variety and relationships of Solanum lasiocarpum.
Pp. 412-415 in Solanaceae: biology and systematics, ed. W. G. D’Arcy. New York: Columbia University Press.
Heiser, C.B., Jr. 1987. Origins of Solanum lasiocarpum and S. repandum.
Amer. J. Bot. 74: 1045-1048.
Heiser, C.B., Jr. 1996. Reappraisal of Solanum ferox, S. lasiocarpum, and S. repandum.
Solanaceae Newsletter 4(2): 44-50.
Bohs, L. 2004. A chloroplast DNA phylogeny of Solanum section Lasiocarpa (Solanaceae).
Syst. Bot. 29: 177-187.
Bohs, L. 2005. Major clades in Solanum based on ndhF sequences.
Pp. 27-49 in R. C. Keating, V. C. Hollowell, & T. B. Croat (eds.), A festschrift for William G. D’Arcy: the legacy of a taxonomist. Monographs in Systematic Botany from the Missouri Botanical Garden, Vol. 104. Missouri Botanical Garden Press, St. Louis.
Levin, R.A., N.R. Myers, & L. Bohs 2006. Phylogenetic relationships among the "spiny" solanums (Solanum subgenus Leptostemonum).
Amer. J. Bot. 93: 157-169.
chloroplast ndhF sequence: GenBank AF224072 (voucher: Olmstead S-100, WTU) chloroplast trnS-G sequence: GenBank AY555459 (voucher: Bohs 2898, UT) chloroplast trnT-F sequence: GenBank AY266237 (voucher: Bohs 2898, UT) chloroplast trnT-F sequence: GenBank AY266250 (voucher: Stoutamire s.n., IND from Heiser S249) nuclear ITS sequence: GenBank AF244722 (voucher: Olmstead S-100, WTU) nuclear ITS sequence: GenBank AY263456 (voucher: Stoutamire s.n., IND from Heiser S249) nuclear waxy (GBSSI) sequence: GenBank AY562953 (voucher: Bohs 2898, UT)
The following commentary is largely taken from Whalen et al. (1981):
Solanum candidum is similar to S. quitoense, but differs in having denser spines and reddish, persistently hairy fruits with sparse cream or yellowish fruit pulp. Solanum candidum is also similar to S. hirtum. The latter species differs in its smaller leaves and fruits and its sessile and usually gland-tipped stem stellae.
Solanum candidum shows a striking clinal pattern of variation in Mexico and Central America. In the northwestern Mexican states of Somora, Chihuahua, Sinaloa, and Nayarit, most plants have relatively inconspicuous pubescence, numerous, fine cauline prickles, long pedicels, large corollas, and short fruit hairs. In Figure 21 of Whalen et al. (1981), variation of these characters in the four northwestern Mexican states is compared with that found in Guatemala and Belize, using measurements taken from herbarium collections. The differences are of magnitude that might justify recognition of distinct taxonomic entities, were the extreme forms not interconnected by a clinal series of intermediate populations. To visualize this cline, data on variation in nine characters was subjected to principal component analysis (PCA). The second principal component, which explained 12.3% of the total variance, best expressed the clinal variation in S. candidum. PCA-2 values for individual collections are mapped in Figure 22 of Whalen et al. (1981), showing an overall clinal pattern with extreme forms in the Mexican state of Nayarit and in eastern Guatemala. It is tempting to speculate on the significance of this cline, in that it spans the transition from subtropical to tropical environments, but more complete knowledge is needed of the biological functions of the variable characters. It is not presently possible to suggest whether the cline is primary or the result of secondary contact between divergent population systems. In Costa Rica, Panama, Colombia, Ecuador, and Peru, S. candidum seems to be rather sparsely distributed. Plants of this region resemble those of Guatemala, with conspicuous, woolly, yellowish pubescence, but are set apart by a relative paucity of prickles on stems and leaves.