Phylogenetic Analysis of Nepenthaceae, Based on Internal Transcribed Spacer Nuclear Ribosomal DNA Sequences

Abstract

Nepenthaceae, a monotypic family of carnivorous pitcher plants comprising Nepenthes, is widely distributed in Southeast Asia. To determine the phytogeography of Nepenthes in Southeast Asia, and to trace the evolutionary trends of taxonomically important characteristics (i.e., peristomes) of the genus, we analyzed 57 internal transcribed spacer (ITS) nuclear ribosomal DNA (nrDNA) sequences of 56 species of Nepenthes and 1 ITS sequence each of Dionaea muscipula and Ancistrocladus robertsoniorum. To clarify the phylogenetic relationships of Nepenthes, we examined four different methods of phylogenetic tree reconstruction. The resulting tree topologies were mostly consistent with one another except for the basal polytomies. Seven monophyletic subclades could be recognized. Similarities and differences in terms of the positions of taxa between the present study and previous studies were observed. Judging from the phylogenetic trees and distribution area of each species, Borneo appears to be a secondary center of diversification for Nepenthes and species of Nepenthes may have then radiated within the Sunda Shelf of Southeast Asia. The three character states of the peristomes from the upper pitchers were relatively well correlated with the grouping of the species of Nepenthes within seven subclades and showed the limitations of the Danser (1928) system for Nepenthes.