Solanum hirtum
2n=24 (Whalen et al. 1981)
A lowland species, usually below 1000 m but occasionally reaching higher elevations; occurring naturally in scrublands, savannas and forest openings and along streambanks and quebradas; common as a weed in secondary thickets, pastures, roadsides and other disturbed sites; in open sun or partial shade; tolerant of many soil types from poorly drained, fine-textured ones to sand and stony soils; in mesic or sometimes semi-arid situations. From Trinidad, Venezuela and northern Colombia through Central America to Yucatán, Oaxaca, Veracruz and Tamaulipas in Mexio.
Solanum hirtum belongs to the Leptostemonum clade of Solanum (Bohs, 2005). Within Leptostemonum, it belongs to the Lasicarpa 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. hirtum is relatively isolated from the other species of the Lasiocarpa clade (Bohs, 2004). However, data from the nuclear waxy gene place S. hirtum on a clade with S. pseudolulo, S. vestissimum, S. pectinatum, and S. hyporhodium (L. Bohs, unpublished data). There is considerable incongruence between the chloroplast trnT-F and nuclear waxy trees with respect to relationships inferred among species in the Lasiocarpa clade. The reason for this incongruence is not known with certainty, but it may imply a history of hybridization among these taxa. Heiser (e.g., 1972, 1985, 1986, 1987, 1989) has demonstrated that many of the species of section Lasiocarpa can form fertile interspecific hybirds and has even described one of them as a distinct species, S. indianense C. Heiser & J. Soria (Heiser et al., 2005).
Heiser, C.B., Jr. 1972. The relationships of the naranjilla, Solanum quitoense. Biotropica 4: 77-84.
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. 1985. Ethnobotany of the naranjilla (Solanum quitoense) and its relatives. Econ. Bot. 39: 4-11.
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. 1989. Artificial hybrids in Solanum sect. Lasiocarpa.
Syst. Bot. 14: 3-6.
Bohs, L. 2004. A chloroplast DNA phylogeny of Solanum section Lasiocarpa (Solanaceae).
Syst. Bot. 29: 177-187.
Heiser, C., J. Soria, C. Miller, & G. Anderson 2005. A new synthetic allopolyploid naranjilla, Solanum indianense (Solanaceae). Novon 15: 290-292.
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.
nuclear ITS sequence: GenBank AY263462 (voucher: Whalen 730, QCA) nuclear ITS sequence: GenBank AY263458 (voucher: Jones s.n., IND from Heiser S404) nuclear ITS sequence: GenBank AY263464 (voucher: Whalen 737, QCA) nuclear ITS sequence: GenBank AY263463 (voucher: Whalen 735, QCA) nuclear waxy (GBSSI) sequence: GenBank AY996425 (voucher: Whalen 730, QCA) chloroplast trnS-G sequence: GenBank AY998424 (voucher: Whalen 730, QCA) chloroplast trnT-F sequence: GenBank AY266253 (voucher: Jones s.n., IND from Heiser S404) chloroplast trnT-F sequence: GenBank AY266254 (voucher: Whalen 730, QCA)
Solanum hirtum can be distinguished from other members of section Lasiocarpa by its gland-tipped stellate hairs, reflexed calyx lobes, and small leaves and fruits. The hairs do not rub off the ripe fruits.
The following commentary is taken from Whalen et al. (1981):
Solanum hirtum is the most widespread and variable species of section Lasiocarpa. Extending from Mexico through Cental America, Colombia, and Venezuela to Trinidad, its diverse forms have received at least six species names. The most variable network of populations is found in northern Colombia and Venezuela, where the following extremes can be recognized.
Many coastal lowland populations in Venezuela consist of unarmed or sparsely prickly plants with broad, sinuate-repand leaves and pentagonal-stellate corollas with well developed interpetalar tissue. This form has been called S. obtusifrons Bitter.
In the interior llanos of Venezuela, plants are often coarsely armed with unusually large and numerous, broad-based prickles on stems, petioles, and leaves (S. orinocense Dunal).
A high elevation race in the cordillera of western Venezuela has the large, coarse prickles common in the llano plants, a dense vestiture of stalked stellate hairs, and fleshy protuberances at the base of the calyx in fruit (S. timotense Pitt.). This form extends into northeastern Colombia in mountains of Santander and Norte de Santander.
Plants with prominently velutinous calyces occur sporadically in Trinidad. Vahl’s type specimen of S. hirtum is one of these.
In Colombia, collections from the Magdalena Valley and northern coastal lowlands from Cartagena to Santa Marta have densely acicular-prickly stems and stellae with capitate-glandular midpoints on stems and pedicels. The stellae of adaxial leaf-surfaces often appear simple with reduced lateral rays and relatively elongate midpoints.
Many other forms more local in occurrence could be described. It would be counterproductive to attempt to provide formal names for the many variants of S. hirtum. Even the major races listed above are not clearly delimitable entities. Instead, a complex mosaic of variation is observed in which certain regional norms emerge. Studies of plants growing under uniform greenhouse conditions have confirmed that differences among representative accessions of forms 1, 3, and 5 are genetically controlled and cannot be explained as environmentally induced variation.
The high altitude form (3) is particularly interesting, because it is the only race with clear ecological integrity and is the most distinctive morphologically. A multivariate mapping of variation in seven characters, based on principal component analysis, has been used to visualize the distribution of this race. Characters scored include cauline prickle length, width of cauline prickles at base, cauline prickle density, stalk length of cauline stellae, stalk length of pedicel stellae, glandularity of pedicel stellae, and presence of calyx protuberances. Most of the high elevation plants have extreme values on the first principal component axis, but a few of them are much like lowland forms. Conversely, occasional lowland populations approach their highland relatives in morphology. The distinction between the highland race and low elevation populations of S. hirtum is not sharp. The actual mosaic pattern of variation is illustrated in Figure 28 of Whalen et al. (1981). The relation between low and high-elevation population systems may be one of incipient speciation.
Heiser (1972) reported a strong barrier to crossability between accessions of S. hirtum from Costa Rica and Trinidad, plants rather similar in morphology. In the present study, crosses have been attempted between accessions of races 1 and 3, highly divergent forms both morphologically and ecologically. These crosses were uniformly successful and produced abundant viable seed, but fertility of hybrid plants has not yet been tested. Thus, initial evolution of internal crossability barriers may bear little relation to patterns of morphological and ecological differentiation. Solanum hirtum will be an interesting subject for studies on early stages of speciation in section Lasiocarpa.
The spotty distribution of S. hirtum in Mexico and Central America may reflect relatively recent multiple introductions from South America. Centers of establishment in Central America are Honduras, the state of Guanacaste in Costa Rica, and the Darién of Panama. In and around each of these centers, populations of the species are strikingly uniform in morphology. Between them, the distribution appears to be sharply discontinuous. In Mexico, separate introductions may have occurred in Yucatán and Veracruz. Extensive variation in Colombia and Venezuela and the presence of related species there point to that region as the center of origin of S. hirtum.
An interesting pattern of fruit-bursting has been observed in accessions of S. hirtum under greenhouse cultivation. The pericarp of ripe berries regularly splits in a neat, circumscissile fashion. The suture may be either equatorial or meridional. Since this behavior has not been seen in the field, we assume that berries are generally harvested by frugivores before reaching this stage. What significance this regular pattern of fruit-bursting may have in the reproductive biology of the species is unknown.