The phylogenetic position of the morphologically unusual Pleurostichidium falkenbergii (Rhodomelaceae, Rhodophyta) based on plastid phylogenomics

Abstract

Pleurostichidium falkenbergii is an obligate epiphyte on Xiphophora chondrophylla and is endemic to northern New Zealand. This monotypic genus is characterised by having dorsiventral and laterally compressed thalli with 20 pericentral cells and complete cortication, adventitious trichoblasts, spherical spermatangial branches formed from cortical cells, and stichidia with up to 19 whorled tetrasporangia. This unusual combination of morphological characters among the Rhodomelaceae led to its placement in a separate tribe Pleurostichidieae. The tribal phylogenetic placement has been investigated only using 18S rRNA and remains uncertain. We investigated the phylogenetic affinities of P. falkenb..