Phylogeny and Provisional Classification of the Solanaceae Based on Chloroplast DNA

A phylogenetic analysis of the Solanaceae based on chloroplast DNA variation is presented. Restriction site maps were determined for 79 species (52 genera) for 11 restriction enzymes. Sequences of two chloroplast genes, rbcL and ndhF, were determined for 30 and 36 species respectively, including six genera not sampled in the restriction site survey. The results are presented as three separate analyses examining relationships at different hierarchical levels. The resulting cladograms provide the basis for a provisional new infrafamilial classification. This classification includes seven subfamilies, three of which are further subdivided into tribes, two of which are further subdivided into subtribes. This classification is compared to the contemporary classification of Hunziker et al. (this volume). Introduction The roots of modern plant classification spread deeply into the history of western civilization, but the starting point for modern classification and nomenclature dates to Linnaeus (1753). Linnaeus held a typological view of species, consistent with the belief in special creation prevalent at the time, but he grouped species by similarities into a hierarchical classification. However, Darwin (1859) first understood that a hierarchical classification has a biological foundation in the evolutionary history that connects species in the form of a phylogenetic tree. For more than a century, taxonomists have pursued Darwin's goal of "all true classification being genealogical." Many of the groups recognized in Linnaeus' work (1753) are included in classifications today, because the similarities he recognized represent homologies and reveal evolutionary history. Progress toward the goal of producing phylogenetic classifications has accelerated greatly in recent years due to three advances: 1) an explicit framework for interpreting phylogeny (Hennig 1966); 2) the incorporation of modern methods from molecular biology that take advantage of the enormous amount of data available in the DNA of organisms; and 3) the development of computer technology that has allowed the analysis of such large amounts of data. Revised classifications reflecting these principles and methods have appeared for the Lamiaceae (Cantino et al. 1992) and Asteraceae (Bremer & Jansen 1992). The history of Solanaceae classification (D'Arcy 1979, 1991) is typical of many large families of flowering plants (e.g., Scrophulariaceae, reviewed in Olmstead & Reeves 1995) in having a core of genera assigned to the family in essentially all treatments and a number of allied genera or groups of genera that are alternatively treated as either belonging to the family, belonging to other related families, or segregated into their own families. Often these latter taxa exhibit unusual combinations of characters found in another family or lack characters typical of the family. It is these problematic taxa for which molecular data often prove most helpful (Keeley & Jansen 1991; Olmstead & al. 1993a; Bremer & al. 1994; Olmstead & Reeves 1995). Examples of problematic genera in the history of classification of the Solanaceae include the zygomorphic-flowered members of the polyphyletic tribe Salpiglossidae, placed in the Scrophulariaceae by Bentham (1876), Nolana, placed in its own family in many treatments (e.g., Thorne 1992), and Goetzea and related genera, also placed in their own family in most treatments (e.g., D'Arcy 1991; Thorne 1992). In addition there are several enigmatic and rarely collected genera, including Atrichodendron, Duckeodendron, Lithophytum, Parabouchetia, Paiuia, Sclerophylax,