Patterns of diversification and ancestral range reconstruction in the Southeast Asian-Pacific angiosperm lineage <I>Cyrtandra</I> (<I>Gesneriaceae</I>)

Abstract

The genus <I>Cyrtandra</I> is the largest in the <I>Gesneriaceae</I> family and is one of the most widely dispersed plant genera in southeast Asia and the Pacific. Species of <I>Cyrtandra</I> are morphologically diverse but characters are often homoplastic causing considerable difficulty in defining monophyletic classification units. In this study, we used molecular phylogenetic analysis of 88 taxa representing approximately 70 species to construct a well-resolved evolutionary hypothesis for <I>Cyrtandra</I>. Diversification rates analysis and ancestral range analysis were also conducted to infer timing of major lineage divergences and geographic origin of these lineages, principally among Pacific species. Using these data, we compared existing classification schemes to better understand the applicability of current taxonomy. Divergence time estimates support a diversification of the Pacific clade at approximately 20 MYBP. Although the origin of the Pacific lineage remains unresolved, ancestral range reconstruction analysis supports Fiji as the most likely &quot;first-step&quot; into the Pacific with subsequent dispersals to Hawai&#39;i, and other archipelagos. A greater Fiji-Samoa region, corresponding with Takhtajan&#39;s Fijian Region, is implicated as a major Pacific region interface and possibly a center of origin for expansion of <I>Cyrtandra</I> throughout the Pacific. Among South Pacific taxa sampled, several supported clades in our evolutionary hypothesis are characterized by distinct morphological traits possibly warranting sectional rankings. Relationships among Hawaiian taxa are less resolved and the distributions of species within this clade do not consistently correspond to existing sectional rankings. More detailed, population-level research is needed to clarify these relationships. We argue that future sectional classifications should correspond with monophyletic lineages and that species-level relationships should be more closely studied within these lineages.