2n = ploidy missing =24 voucher missing = (Spooner & Hijmans 2001)
Mexico: Chiapas; Guatemala; 2740-3800 m; typically growing in moss in upland pine and fir forests, frequently associated with Acaena elongata L., Alchemilla pectinata HBK, or Pernella ciliata (Schltdl. and Cham.) Small. Populations often contain hundreds of individuals in all stages of development, from emerging plants to plants with mature fruits, but fruiting plants can be scarce.
Solanum clarum belongs to the potato clade of Solanum (Bohs, in press). Spooner and Sytsma (1992) placed S. clarum and all other North and Central American diploids (exclusive of S. bulbocastanum, S. cardiophyllum, and S. verrucosum) in the basal “clade 1” of section Petota based on chloroplast DNA restriction site data. Spooner et al. (2004) placed S. clarum and S. morelliforme in the Morelliforme group based on morphological and AFLP data (Lara-Cabrera and Spooner, in press a,b). Hawkes (1956) erected Solanum ser. Morelliformia to accommodate the species S. morelliforme, and Correll (1962) described Solanum ser. Clara to accommodate the species S. clarum. Correll (1962) and Bukasov (1978) maintained this taxonomy but Hawkes (1963, 1990) placed S. clarum and S. bulbocastanum into ser. Bulbocastanum while maintaining a monotypic ser. Morelliformia (see Plate 1 of Spooner et al. 2004). Solanum clarum and S. morelliforme form a clade according to cpDNA data (Spooner and Sytsma 1992). They occur in similar habitats; S. morelliforme is an epiphyte, and S. clarum rarely grows as an epiphyte but more commonly in the shade of trees in moss in epiphytic-like conditions. The species can be crossed with each other, but with great difficulty, and the hybrids exhibit chromosomal structural differences and sterility in the F2 generation (Marks 1968). Marks (1969) demonstrated by pachytene analysis that the species share characteristic large telochromomeres (although on different chromosomes) unknown in the rest of sect. Petota. Nee (1999) was the first to ally both species to ser. Morelliformia, and Spooner et al. (2004) recognized them under the informal Morelliforme group.
Solanum clarum is very distinctive with its simple leaves and relatively small stature (stems 2-3 mm wide at base, 0.15-0.35 m tall). Solanum bulbocastanum and S. morelliforme are the only other wild potato species from North and Central America with simple leaves. Solanum morelliforme is the most similar species, but differs from S. clarum by its lanceolate to ovate-lanceolate leaves (ovate in S. clarum). Solanum bulbocastanum is a much larger plant (stems 3-6 mm wide at base, plants up to 1 m tall) and has cream to yellow corollas (white or white tinged with purple in S. clarum and S. morelliforme).
Lara-Cabrera, S. & D.M. Spooner Taxonomy of Mexican diploid wild potato (Solanum sect. Petota) species: AFLP data.
Plant Syst. Evol.
Lara-Cabrera, S. & D.M. Spooner Taxonomy of Mexican diploid wild potato (Solanum sect. Petota) species: morphological and microsatellite data.
Monogr. Syst. Bot., Missouri Bot. Gard.
Hawkes, J.G. 1956. A revision of the tuber-bearing Solanums.
Rep. Scott. Pl. Breed. Stn. 1956: 37-109.
Correll, D.S. 1962. The potato and its wild relatives.
Contr. Texas Res. Found., Bot. Stud. 4: 1-606.
Hawkes, J.G. 1963. A revision of the tuber-bearing Solanums. II.
Scott. Pl. Breed. Sta. Rec. 1963: 76-181.
Marks, G.E. 1968. Structural hybridity in a tuberous Solanum hybrid.
Canad. J. Genet. Cytol. 10: 18-23.
Marks, G.E. 1969. The pachytene chromosomes of S. clarum.
Caryologia 22: 161-167.
Bukasov, S.M. 1978. Systematics of the potato (In Russian).
English translation of article first appearing in Trudy Prikl. Bot. 62: 3-35. In Systematics, Breeding, and Seed Production of Potatoes, ed. V. S. Kothetar, translator, A. K. Dhote, 1-42. New Delhi: Amerind Publ. Co.
Hawkes, J.G. 1990. The potato: evolution, biodiversity and genetic resources.
Oxford: Belhaven Press.
Spooner, D.M. & K.J. Sytsma 1992. Reexamination of series relationships of Mexican and Central American wild potatoes (Solanum sect. Petota): evidence from chloroplast DNA restriction site variation.
Syst. Bot. 17:432-448.
Nee, M. 1999. Synopsis of Solanum in the New World.
Pp. 285–333 in M. Nee, D. E. Symon, R. N. Lester & J. P. Jessop (eds.), Solanaceae IV: Advances in Biology and Utilization. Royal Botanic Gardens, Kew.
Spooner, D.M. & R.J. Hijmans 2001. Potato systematics and germplasm collecting, 1989-2000.
Amer. J. Potato Res. 78:237-268; 395.
Lara-Cabrera, S.I. 2001. Taxonomy of Mexican diploid wild potato (Solanum sect. Petota) species: a morphological and molecular study.
Ph.D. Thesis, Plant Breeding and Plant Genetics Program, University of Wisconsin-Madison.
Spooner, D.M., R.G. van den Berg, A. Rodríguez, J. Bamberg, R.J. Hijmans, & S.I. Lara-Cabrera 2004. Wild potatoes (Solanum section Petota; Solanaceae) of North and Central America.
Syst. Bot. Monog. 68: 1-209 + 9 plates.
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.
Chloroplast DNA restriction site data available in: Spooner and Sytsma (1992). AFLP, morphological, and microsatellite data listed in: Lara-Cabrera (2001).