Circumscription and phylogenetic relationship of Prostanthera densa and P. marifolia (Lamiaceae)

Abstract

Prostanthera densa A.A.Ham. and P. marifolia R.Br. (Lamiaceae) are endemic species with restricted distributions within the near-coastal regions of New South Wales (Australia). Prostanthera marifolia was previously presumed extinct, but is now known from a small population in the Manly-Warringah area of metropolitan Sydney, and is morphologically very similar to P. densa. Prostanthera densa is known from five disjunct populations, distributed from Port Stephens (in the north) to Jervis Bay (in the south). The sequence variation of two chloroplast spacer regions, trnT-trnL and psbA-trnH, and the external transcribed spacer (ETS) region of nuclear ribosomal DNA were analysed to evaluate the phylogenetic relationship and taxonomic integrity of these species. Although trnT-trnL data were uninformative, trees generated from psbA-trnH data provided support for recognising P. marifolia as a distinct species sister to P. densa. A multivariate evaluation of the variation in morphological characters also supported the distinction of these two morphologically similar and closely related species. The ETS data indicated that each of the disjunct populations of P. densa were genetically isolated. Since there was no gene flow between populations of P. densa, it was concluded that the conservation of this species requires all populations to be protected.