Resolving intergeneric relationships in the aervoid clade and the backbone of Ptilotus (Amaranthaceae): evidence from whole plastid genomes and morphology

Abstract

The informally named “aervoid clade” in Amaranthaceae includes ~134 species in five genera: Ptilotus (~120 spp.), Aerva (11 spp.) and the monotypic Nothosaerva, Omegandra, and Kelita. The relationships of the small aervoid genera to the large genus Ptilotus, and relationships between major clades within Ptilotus, are poorly resolved. The aims of this study were to: (1) elucidate relationships between genera and within Ptilotus using a phylogenomic approach; (2) identify morphological characters within each genus to help delimit generic boundaries; and (3) provide an updated taxonomic framework for the aervoids. A well-supported coding DNA sequence (CDS) phylogeny was constructed for 36 aervoid and 5 outgroup species based on 69 gene sequences derived from assembled whole-plastid genomes. The CDS tree was used to constrain relationships on a larger phylogeny based on Sanger-sequenced ITS and matK for 135 taxa, comprising near-comprehensive sampling within the aervoids. Both datasets were analysed using maximum likelihood and Bayesian inference. Morphological characters were assessed from herbarium specimens. Our study demonstrates that Aerva is polyphyletic; this is resolved by reinstating Ouret and erecting a new genus, Paraerva. Kelita is found to be deeply nested within Ptilotus and is formally synonymised. The well-resolved phylogeny of Ptilotus presented here will inform future studies in biogeography and character evolution. A taxonomic treatment is provided for all aervoid genera, and new combinations are made.