Pasella M.M., Verbruggen H., Nelson W.A. & Diaz-Tapia P.
Resolving the phylogenetic position of Pleurostichidium (Rhodomelaceae, Rhodophyta) based on plastid phylogenomics
Phycologia: submitted


Pleurostichidium falkenbergii is an obligate epiphyte on Xiphophora chondrophylla and is endemic to northern New Zealand. It is characterized by an unusual morphology among the Rhodomelaceae that led to the establishment of the tribe Pleurostichidieae. Its phylogenetic relationships have only been investigated using the 18S rRNA gene and remain uncertain because of limited taxon sampling and the poor resolution of that marker in Rhodomelaceae. In this work we aim to investigate the phylogenetic affinities of Pleurostichidium using a phylogenomic approach. We sequenced and assembled its chloroplast genome and inferred a phylogenetic tree along with that of 45 other rhodomelacean species and 10 outgroup taxa. Pleurostichidium was placed with high support in a clade containing the tribes Pterosiphonieae, Dipterosiphonieae, Herposiphonieae, and a clade with two species morphologically assigned to Polysiphonia and Melanothamnus but genetically unrelated to the true Polysiphonia and Melanothamnus lineages. The genus Pleurostichidium was placed as sister to the Pterosiphonieae with moderate support. Considering our results and the morphological characters of Pleurostichidium, we propose to maintain the tribe Pleurostichidieae for this unusual species.

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