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In phylogenetic analysis, direction of ingroup evolution depends on outgroup, therefore, the determination of correct outgroup is very critical. In the current study, effect of different outgroups on tree topology within Solanaceae was examined using Bayesian analysis. Different outgroups were selected from closely related families of Solanaceae (Convolvulaceae, Hydrolaceae and Montiniaceae), distantly related families (Acantaceae, Scrophularaceae and Boraginaceae) and more distantly related group (Gymnospermic families; Cycadaceae and Pinaceae). Single taxa from each family, multiple taxa from a single genus and multiple taxa from different genera of the same sister family were selected to evaluate their resolving power. The single taxa of a genus belong to Convolvulaceae produced more consistent result as compared to the multiple taxa of the single genus. In addition, single taxa produced similar tree topology as produced by multiple taxa of different genera. Among single taxa, Evolvulus pilosus, observed to be the best outgroup because it resolved the associations between genus, tribes, and subfamilies within Solanaceae followed by Humbertiama dagascariensis. The lineages established by the successful outgroups suggest the evolutionary pattern within Solanaceae is Cestroideae to Petunoideae to Solanoideae. Distantly related outgroup was unable to resolved the tree topology. It may be suggested that for lower level taxonomical relationships of Solanaceae, Evolvulus pilosus could be used as outgroup to infer true associations.
Keywords: Ingroup; Outgroup; Phylogenetics; rbcL; Solanaceae