Mitochondrial and chloroplast DNA‐based phylogeny of Pelargonium (Geraniaceae)

Abstract

Overall phylogenetic relationships within the genus Pelargonium (Geraniaceae) were inferred based on DNA sequences from mitochondrial(mt)-encoded nad1 b/c exons and from chloroplast(cp)-encoded trnL (UAA) 5' exon-trnF (GAA) exon regions using two species of Geranium and Sarcocaulon vanderetiae as outgroups. The group II intron between nad1 exons b and c was found to be absent from the Pelargonium, Geranium, and Sarcocaulon sequences presented here as well as from Erodium, which is the first recorded loss of this intron in angiosperms. Separate phylogenetic analyses of the mtDNA and cpDNA data sets produced largely congruent topologies, indicating linkage between mitochondrial and chloroplast genome inheritance. Simultaneous analysis of the combined data sets yielded a well-resolved topology with high clade support exhibiting a basic split into small and large chromosome species, the first group containing two lineages and the latter three. One large chromosome lineage (x = 11) comprises species from sections Myrrhidium and Chorisma and is sister to a lineage comprising P. mutans (x = 11) and species from section Jenkinsonia (x = 9). Sister to these two lineages is a lineage comprising species from sections Ciconium (x = 9) and Subsucculentia (x = 10). Cladistic evaluation of this pattern suggests that x = 11 is the ancestral basic chromosome number for the genus.

The phylogeny of Monsonia L. (Geraniaceae)

“…The rbcL cpDNA region and mtDNA nad1b/c exon of just a few representatives of the genus have been sequenced (Price and Palmer 1993, Bakker et al 2000a, Soltis et al 2000. These study showed that Monsonia and Sarcocaulon are either sister genera or congeneric and sister to the other three (or four) genera in the Geraniaceae.…”

Phylogeny of Pelargonium (Geraniaceae) Based on DNA Sequences from Three Genomes

“…On the other hand, excluding P. karooicum from the analysis fixes P. transvaalense in a position sister to a (Subsucculentia(Ciconium)) clade with 69% jackknife support (not shown). Previously, we interpreted the observation that our P. karooicum material has a P. caylae-type chloroplast, a Subsucculentia-type mitochondrion as well as a Subsucculentia karyotype (x = 10) as indicative of chloroplast capture from P. caylae (Bakker & al., 2000b). However, low support values for the incongruent P. karooicum clades (Fig.…”

“…-Congruence among phylogenies derived from the different genomes is generally high with only three well-supported incongruencies found between the cpDNA trnL-F and rDNA ITS phylogenies and one between the trnL-F and nad1 phylogeny (Bakker & al., 2000b). Given that 149 taxa are involved and that "paternal leakage" and biparental inheritance have been reported in some species of Pelargonium (Tilney-Bassett, 1963;Kuroiwa & al., 1993;Nagata & al., 1997), the apparent rarity of topological incongruencies is somewhat surprising.…”

“…Nucleotide substitution rates in plant mitochondrial DNA are generally considered to be too low to be suitable for phylogenetic reconstruction at lower taxonomic levels (e.g., Palmer, 1992). However, in Pelargonium, rates of mtDNA nucleotide substitution have been found to be substantially elevated with respect to other angiosperm groups studied so far (Bakker & al., 2000b; enabling reconstruction of a specieslevel phylogeny from the perspective of all three genomes.…”

“…The remainder of the genus comprises approximately 55 species with chromosomes of 1.5-3.0 µm long (Albers & van der Walt, 1984;Gibby & Westfold, 1986;Gibby, 1990) and includes woody and succulent (sub)shrubs as well as herbaceous annuals. In a previous study (Bakker & al., 2000b) we reported an overall phylogenetic hypothesis for Pelargonium (28 species) based on cpDNA trnL-F and mtDNA nad1 gene sequences. Here we extend these datasets along with data from the rDNA ITS regions, including approximately half of the species known to Pelargonium.…”