2n=2x=24 [voucher Ochoa 11855 (CUZ)]; Hijmans et al. 2007
Endemic to central to southern Peru (Depts. Ayacucho, Cuzco, Huánuco, Junín and Pasco), in moist habitats, at forest edges; 670-4150 m in elevation.
Solanum laxissimum is a member of Solanum sect. Petota Dumort., the tuber-bearing cultivated and wild potatoes. Within sect. Petota, Solanum laxissimum is a member of a distinctive group of species formerly classified in series Conicibaccata (see below). On a higher taxonomic level, it is a member of the informally-named Potato Clade, a group of perhaps 200-300 species that also includes the tomato and its wild relatives (Bohs, 2005).
Hawkes (1990) treated Solanum laxissimum as one of 40 species in Solanum sect. Petota series Conicibaccata Bitter, a group containing diploids (2n = 24), tetraploids (2n = 48), and hexaploids (2n = 72). The polyploids are mainly distributed from southern Mexico south to central Peru (one species in northern Bolivia), and the diploids from northern Peru to central Bolivia.
The species boundaries and relationships of members of series Conicibaccata have been studied using plastid DNA restriction sites (Castillo and Spooner, 1997), morphology (Castillo and Spooner, 1997; Fajardo et al., 2008), AFLPs (Jiménez et al., 2008), nuclear DNA (“waxy”) sequence data (Spooner et al., 2008), other nuclear DNA sequence data (in preparation by Fajardo and Spooner), and monographic studies (Hawkes, 1990; Hawkes and Hjerting, 1989; Ochoa, 1990, 1999). The plastid DNA restriction site and morphological data divide the diploids and polyploids into two clades or phenetic groups, respectively, but the morphological separation generally depends on the use of character states that sometimes overlap in range. The DNA sequence data show the polyploids to be of allopolyploid origin from the diploid members of the series and members of species outside of the series.
A monographic study in progress by Fajardo and Spooner, using the above data, and herbarium specimens, will recognize only 17 species. All are very similar, united as a group by conical fruits, leaves with generally parallel sided morphology, and narrowly ovate to elliptical leaflets. However, some unrelated species also have conical fruits, such as the Mexican diploid species S. hintonii Correll, S. lesteri Hawkes and Hjert. and S. trifidum Correll; the Mexican hexaploid species S. iopetalum (Bitter) Hawkes; and the Bolivian species S. circaeifolium Bitter. An additional problem is that some species possess ovoid fruits that are not absolutely distinct from the conical fruits of the above species or the globose fruits more common in the majority of the members of sect. Petota.
Solanum laxissimum is characterized by its acute or attenuate elongated leaflets with purple color sometimes present abaxially, sparsely pubescent leaves, winged stem, glabrous to subglabrous calyx, and pentagonal to rotate, often purple corolla.
Bohs, L. 2005. Major clades in Solanum based on ndhF sequence data. Pp. 27-49. In: R. C. Keating, V. C. Hallowell, and T. B. Croat (eds.), A Festschrift for William G. D’Arcy: A Legacy of a Taxonomist. Missouri Botanical Garden, St. Louis.
Castillo, R. and D. M. Spooner. 1997. Phylogenetic relationships of wild potatoes, Solanum series Conicibaccata (sect. Petota). Syst. Bot. 22: 45-83.
Fajardo, D., R. Castillo, A. Salas, and D. M. Spooner. 2008. A morphometric study of species boundaries of the wild potato Solanum series Conicibaccata: a replicated field trial in Andean Peru. Syst. Bot. 33: 183-192.
Fajardo, D., and D. M. Spooner. 2011. Phylogenetic relationships of Solanum series Conicibaccata and related species in Solanum section Petota inferred from five conserved ortholog sequences. Syst. Bot. 36:163-170.
Hawkes, J. G. 1990. The potato, evolution, biodiversity and genetic resources. Washington: Belhaven Press.
Hawkes, J. G. and J. P. Hjerting. 1989. The potatoes of Bolivia: their breeding value and evolutionary relationships. Oxford Univ. Press, Oxford, UK.
Hijmans, R., T. Gavrilenko, S. Stephenson, J. Bamberg, A. Salas and D. M. Spooner. 2007. Geographic and environmental range expansion through polyploidy in wild potatoes (Solanum section Petota). Global Ecol. Biogeogr. 16: 485-495.
Jiménez, J. P., A. Brenes, A. Salas, D. Fajardo, and D. M. Spooner. 2008. The use and limits of AFLP data in the taxonomy of polyploid wild potato species in Solanum series Conicibaccata. Conserv. Genet. 9: 381-387.
Ochoa, C. M. 1990 [actual release date 13 June, 1991]. The potatoes of South America: Bolivia. Cambridge University Press, Cambridge, New York.
Ochoa, C. M. 1999. Las papas de sudamerica: Peru (Parte I). Lima, Peru: International Potato Center.
Spooner, D. M., F. Rodríguez, Z. Polgár, H. E. Ballard Jr., and S. H. Jansky. 2008. Genomic origins of potato polyploids: GBSSI gene sequencing data. The Plant Genome, a suppl. to Crop Sci. 48(S1): S27–S36