Hedyotis, Oldenlandia and related genera (Rubiaceae: Spermacoceae) in Australia: new genera and new combinations in an Asian-Australian-Pacific lineage.
Hedyotis, Oldenlandia and related genera (Rubiaceae: Spermacoceae) comprise a morphologically recognisable group within Spermacoceae, characterised by the presence of raphides, more or less fimbriate stipules, 4-merous flowers, bicarpellate gynoecia, multiovulate locules, peltate placentas and (generally) tricolporate pollen, but generic-level taxonomy within the group has long been problematic. Recent molecular phylogenetic studies have made significant progress in our understanding of generic limits in the group internationally but have included little Australian material. This study includes broad geographic sampling and near complete representation of Australian taxa in maximum likelihood and Bayesian phylogenetic analyses of chloroplast (rps16, petD) and nuclear ribosomal (ITS, ETS) nucleotide sequence data to infer the phylogeny of the Spermacoceae and resolve the generic-level classification of Australian taxa in the group. Two Australian species (Hedyotis novoguineensis, H. philippensis) were placed in Hedyotis. All remaining native Australian taxa currently accepted in Hedyotis, Oldenlandia and Synaptantha were placed within a large clade with an Asian-Australian-Pacific distribution. This clade includes Debia, Dimetia, Involucrella, Kadua, Exallage, Leptopetalum, Scleromitrion and Synaptantha, with Australian taxa included in clades corresponding to the latter four genera. The remaining native Australian species currently accepted in Oldenlandia are placed in two additional clades within the Asian-Australian-Pacific clade, and two new endemic Australian genera, Dolichocarpa and Paranotis, are here described to accommodate them. Oldenlandia s.str. is represented in Australia only by the introduced weed O. corymbosa. The morphology and geographic distribution of genera represented in Australia is discussed. New combinations in Scleromitrion and recommendations for accepted names in Exallage and Leptopetalum in Australia are provided, as is a key to the genera of the Spermacoceae (excluding the Spermacoce clade) in Australia.