Phylogeny of the Cyphomandra clade of the genus Solanum (Solanaceae)

Solanum is one of the largest angiosperm genera, with approximately 1,500 species distributed worldwide. The genus includes important economic plants such as the tomato, potato, and eggplant, as well as a number of lesser-known cultivated species such as the pepino (S. muricatum Aiton), naranjilla (S. quitoense Lam.), cocona (S. sessiliflorum Dunal), and tree tomato (S. betaceum Cav.). Although its large size, morphological complexity, and largely tropical distribution have hindered taxonomic understanding of the genus, molecular approaches are proving useful in elucidating its overall phylogenetic structure. For instance, sequence data from the chloroplast ndhF gene as well as the nuclear ITS and waxy regions have identified at least twelve major clades within Solanum with high bootstrap support (Bohs & Olmstead, 2001; Bohs, 2005; Weese & Bohs, 2007). Several of these clades conform to infrageneric groups recognized by previous systematists on the basis of morphological similarity. Others, however, represent novel groupings that have not been suggested previously. The Cyphomandra clade (sensu Bohs, 2005 and Weese & Bohs, 2007) is one of these well-supported major groups. It encompasses about 50 neotropical species that have been placed into three sections: Solanum section Pachyphylla (Dunal) Dunal, S. section Cyphomandropsis Bitter, and S. section Glaucophyllum A. Child. All taxa of the clade are woody shrubs or small trees and most have relatively small anther pores that do not ultimately open into longitudinal slits. The most consistent morphological synapomorphy of the group is the presence of very large chromosomes and large amounts of nuclear DNA, which have been found in all species of the clade investigated to date (Roe, 1967; Pringle & Murray, 1991a; Moscone, 1992; Bohs, 1994, 2001). Solanum section Pachyphylla was formerly recognized as the genus Cyphomandra Sendtn. and includes the cultivated tree tomato, S. betaceum. Species of this section are found in mesic forests from Mexico to northern Argentina and southeastern Brazil. The morphological synapomorphy that defines section Pachyphylla is the presence of enlarged anther connectives (Sendtner, 1845; Fig. 1A–D) that function in at least some species as floral osmophores to attract male euglossine bees (Gracie, 1993; Sazima & al., 1993). In addition, many species of section Pachyphylla have a distinctive branching pattern and architecture that conforms to Prévost’s model in the architectural scheme of Hallé & al. (1978; see Bohs, 1989, 1994 for details). A taxonomic monograph of the genus Cyphomandra was published in 1994 (Bohs, 1994). The 32 recognized species were placed into five provisional species groups, with three species not placed in any group. Molecular data subsequently showed that the genus Cyphomandra is nested within Solanum (Olmstead & Palmer, 1992, 1997; Spooner & al., 1993; Bohs & Olmstead, 1997, 1999), and all species of Cyphomandra were transferred to Solanum (Bohs, 1995). A new species, S. maternum Bohs, closely related to the tree tomato, was described in 1997 (Bohs & Phylogeny of the Cyphomandra clade of the genus Solanum (Solanaceae) based on ITS sequence data