Phylogeny and biogeography of Balsaminaceae inferred from ITS sequences

Abstract

Sequences of the internal transcribed spacers (ITS) of nuclear ribosomal DNA were acquired for 112 species of Balsaminaceae worldwide and five species of its closest relatives Marcgraviaceae and Tetrameristaceae. Phylogenetic analyses applying parsimony and distance estimates confirmed the monophyly of Balsaminaceae and suggest the monophyly of Impatiens. Within Impatiens, a few clades are recognized with strong support. Two of the most important clades are the spurless Madagascan endemic group, and the one comprising species with broadly fusiform fruits and the basic chromosome number x = 8, that shows a Southeast Asia, southern India, Africa, and Madagascar connection. Despite recognition of several strongly supported small lineages, ITS data alone could not resolve relationships among most of the lineages with confident support values. ITS phylogenies are therefore of limited taxonomic value for Impatiens. However, ITS phylogenies do reveal that extant Impatiens species are of Southeast Asian origin, from where dispersals to boreal Eurasia and North America, to central Asia and eastern Europe via the Himalayas, and to India and Africa have occurred. The Madagascan Impatiens show an African origin. Molecular phylogenies suggest the ancestral basic chromosome number to be x = 10, and the spurred flowers and elongated linear fruits to be plesiomorphic states in Impatiens. A predominantly descending dysploid chromosome evolution, following dispersal of the clade with broadly fusiform fruits from Southeast Asia to India, Africa, and Madagascar, is also suggested.

Mechanisms of Derived Unitegmy among Impatiens Species

“…A subset of this tree, including those species for which ovule morphology has been reported, is shown in Figure 7. The Yuan et al (2004) phylogeny places the clade including I. hookeriana sister to the clade containing the other four species included in our study, with all five species included on a branch of the larger tree. Our phylogram based on Arabidopsis YABBY and Impatiens and Nymphaea INO amino acid sequences (Figure 4) and an unrooted tree constructed with Impatiens INO intron sequences (data not shown) also have I. hookeriana sister to a clade including the other species in our study.…”

“…Thus, it is possible that the intermediate and unitegmic states are derived among the species we studied. However, in the Yuan et al (2004) phylogeny, additional species that have been reported to have an intermediate integument morphology (e.g., Impatiens arguta [Narayana, 1963]) are placed more basally in the complete Impatiens clade. This finding suggests that transitions between bitegmic, unitegmic, and intermediate integument morphologies have occurred repeatedly during the diversification of Impatiens.…”

“…This finding suggests that transitions between bitegmic, unitegmic, and intermediate integument morphologies have occurred repeatedly during the diversification of Impatiens. The nearest outgroups to the Impatiens clade in the Yuan et al (2004) phylogeny have been reported to be bitegmic (L. Watson and M.J. Dallwitz, http://delta-intkey.com), so the intermediate morphology of more basal Impatiens species is hypothesized to derive from bitegmy.…”

“…The apparent relatively frequent transition between the bitegmic, bifid, and unitegmic states in the early diverging asterids, including the Ebenaceae and Primulaceae (Philipson, 1974), as A subset of the neighbor-joining tree of Yuan et al (2004) showing those species for which integument morphology has been described. Numbers above nodes indicate the highest bootstrap values associated with the indicated clade in the full analysis of Yuan et al (2004).…”

“…Our results suggest that unitegmy has evolved by a combination of the simple merging of integument primordia and a change in the location of subdermal growth rather than by integumentary shifting of the outer integument onto the inner integument. Yuan et al (2004) have assembled an extensive phylogeny of Impatiens using ribosomal internal transcribed spacer sequences from a sample of 111 species. A subset of this tree, including those species for which ovule morphology has been reported, is shown in Figure 7.…”