Phylogeny of the holly grevilleas (Proteaceae) based on nuclear ribosomal and chloroplast DNA

Abstract

The holly grevilleas are an informal grouping of 15 species (19 taxa) of woody shrubs from south-eastern Australia, with a centre of distribution in central to western Victoria. Many of the species are narrowly endemic. The present study is the first molecular-phylogenetic analysis of the group, with the aim of providing an evolutionary framework for assessing species-level taxonomy and conservation priorities. Analyses using the nrDNA internal transcribed spacer (ITS) regions were complicated by the presence of divergent paralogues, including inferred pseudogenes; analyses restricted to presumed orthologous, functional ITS sequences were uninformative. Combined analyses of three chloroplast intergenic spacers (trnQ–5′rps16, trnL–trnF and rpoB–trnC) strongly support the monophyly of a core group of 16 taxa (the ‘southern holly grevilleas’) from Victoria and South Australia. However, nodes outside this group are poorly resolved and poorly supported, and the relationships of taxa from New South Wales and eastern Victoria (the ‘northern holly grevilleas’) are unclear. Among the southern holly grevilleas, the following four distinct and partly sympatric cpDNA clades are identified: the ‘Grevillea ilicifolia’, ‘G. aquifolium’, ‘G. dryophylla’ and ‘G. repens’ clades, among which the earliest and most strongly supported divergence is that of the western-most ‘G. ilicifolia’ clade. Variation in cpDNA is incongruent with current species-level taxonomy, especially for G. aquifolium (polyphyletic), G. montis-cole (polyphyletic, but the two subspecies each monophyletic) and G. microstegia (nested in G. aquifolium). The effects of incomplete chloroplast lineage sorting, gene flow through hybridisation or introgression, and inappropriate taxonomy are possible explanations for this incongruence. The formal conservation listing for some species within the holly grevillea group requires re-evaluation.