The Systematic Placement of the Monotypic Genus Paraisometrum (Gesneriaceae) Based on Molecular and Cytological Data

Paraisometrum, is a monotypic genus endemic to Southwest China, with an uncertain systematic position. To resolve the phylogenetic relationships of Paraisometrum within subfamily Cyrtandroideae, we performed phylogenetic analyses of 116 taxa placed in the subfamily Cyrtandroideae and 7 outgroup species selected from other Gesneriaceae subfamilies. The independent and combined analyses were performed on three DNA datasets: the nuclear internal transcribed spacer regions (ITS) and two chloroplast regions (trnL-F, atpB-rbcL). Maximum Parsimony (MP) and Bayesian Inference (BI) were used for tree construction. The combined three gene dataset strongly support Paraisometrum in a clade containing Oreocharis, Opithandra, Isometrum, Ancylostemon, and Briggsia rosthomii. In the MP tree this lineage is an unresolved polytomy, but BI resolves Paraisometrum as sister to B.rosthomii and the Ancylostemon clade. We did the first chromosome counts of Paraisometrum (2n=34). The diploid number 34 has also been reported for Oreocharis, Opithandra, Briggsia and Ancylostemon, which lends further support to the placement of Paraisometrum in this lineage.