Reticulate evolution, cryptic species, and character convergence in the core East Asian clade of Gaultheria (Ericaceae)

Phylogenetic relationships of 84 samples representing 30 species in the core East Asian clade of the wintergreen group of Gaultheria (Angiospermae: Ericaceae: Gaultherieae) were estimated from separate and combined DNA sequence data from five genic regions (ITS, matK, rpl16, trnL-trnF, and trnS-trnG) with parsimony, likelihood and Bayesian analyses. Two major clades were recovered, one comprising several sections and series with leaves generally more than 1 cm long [the ser. Leucothoides sensu lato (s.l.) clade] and another comprising the species of ser. Trichophyllae, with leaves generally less than 1 cm long. The ITS region yielded little phylogenetic resolution, whereas in the combined chloroplast analysis the samples from individual morphospecies in both clades were often nonmonophyletic. This was postulated to result from reticulate evolution in the ser. Leucothoides s.l. clade, particularly in two specific cases of hybridization and a crown clade with likely chloroplast capture following localized introgression. In the ser. Trichophyllae clade, such nonmonophyly was largely attributed to cryptic species and character convergence resulting at least partly from extreme morphological reduction. The relatively low-elevation habitats in which the species of the ser. Leucothoides s.l. clade generally grow are thought to have promoted opportunities for sympatry and reticulation, whereas the high-alpine habitats of ser. Trichophyllae are more likely to have spawned isolated populations and narrow endemism. As in other Sino-Himalayan plant groups, overall low sequence divergence and reticulate evolution suggest rapid radiation in the core East Asian clade of Gaultheria.