Molecular Phylogeny of Casuarinaceae Based on rbcL and matK Gene Sequences

Abstract

We present the first overall molecular phylogenetic study of Casuarinaceae on the basis of sequences of two chloroplast genes, rbcL (1310 bp) and matK (1014 bp), using 15 species representing the family. The study included analyses of Ticodendron (Ticodendraceae) and three species of Betulaceae as close relatives, and one species each of Juglandaceae and Myricaceae as outgroups. Analyses based on matK gene sequences, which provided a much better resolution than the analyses based on rbcL gene sequences alone, resulted in a single most parsimonious tree whose topology is almost identical with the strict consensus tree generated by the combined data set of rbcL and matK gene sequences. Results showed that Casuarinaceae are monophyletic, comprising four distinct genera, A//ocasuarina, Casuarina, Ceuthostoma and Gymnostoma, which were not recognized until recently. Within the family, Gymnostoma is positioned at the most basal position and sister to the remainder. Within the remainder Ceuthostoma is sister to the A//ocasuarina-Casuarina clade. Morphologically the basalmost position of Gymnostoma is supported by plesiomorphies such as exposed stomata in the shallow longitudinal furrows of the branchlets, a basic chromosome number x=8 and the gynoecium composed of two fertile, biovulate carpels. The three other genera, A//ocasuarina, Casuarina, and Ceuthastoma, have invisible stomata in the deep longitudinal furrows of the branchlets, a higher basic chromosome number x=9 or 10-14 (unknown in Ceuthostoma), the gynoecium composed of one fertile and one sterile carpel with a single ovule (unknown in Ceuthastoma). The diversity of infructescence morphology found in the latter three genera suggests that they may have evolved in close association with the elaboration of fruit dispersal mechanisms.

Using matK sequence data to unravel the phylogeny of Casuarinaceae

“…The matK results of Sogo et al (2001) do not support the division of Casuarina into clades C1 and C2. This appears to be because their data set (1014 bp) did not include a highly informative region of ca.…”

“…300 bp at the 3 0 end of the matK gene. Inclusion of the Sogo et al (2001) Casuarina sequences in our data set resulted in conspecific samples grouping together in clades C1 and C2 (data not shown).…”

“…2). Additional matK sequences for Ceuthostoma terminale (Sogo et al, 2001) and outgroup taxa Manos and Steele (1997). b Primer designed by Steele and Vilgalys (1994).…”

“…Sogo et al (2001) carried out a study of rbcL and matK sequences in the family; their results support the recognition of four genera, but their study was based on a limited number of species. In this study we looked at 76 species of the 96 recognised in the family.…”

Genetic Analyses of Casuarinas Using ISSR and FISSR Markers

“…Phylogenetic and taxonomic relationships within the species of casuarinas have been studied using the size and number of chromosomes, pattern of geographical distribution (Barlow, 1959(Barlow, , 1983) and diversification in the morphological characteristics (Wilson & Johnson, 1989) to distinguish the members of Allocasuarina and Casuarina. Recently, rbcL and plastid matK sequences were used for the genetic analysis of Casuarinaceae (Sogo et al, 2001) and the study was further extended to decipher the phylogeny of 76 species demonstrating the monophyly of the four genera and examining the relationships within the family (Steane, Wilson & Hill, 2003).…”