Conflicting placements shed doubts on the ordinal status of Peyssonneliales: Is it a clade in the mega diverse Gigartinales?

Gigartinales is a polyphyletic order of red algae, comprising a large diversity of species, several of which have tremendous ecological and economic relevance. Peyssonneliaceae, a clade of red encrusting algae distributed worldwide, was initially placed in Cryptonemiales, later classified in Gigartinales and most recently elevated to ordinal status as Peyssonneliales. The family includes 147 species in 17 genera. Molecular phylogenetic analyses have been used to justify the segregation of Peyssonneliaceae from Gigartinales, but this has been based on more limited gene sampling. Here we include newly sequenced mitochondrial and plastid organellar genomes in a broader phylogenomic analysis of Rhodophyta to elucidate the evolutionary history and discuss the taxonomic validity of Peyssonneliales. Our well‐supported results demonstrate conflicting placements of Peyssonneliaceae, which include its nested placement within Gigartinales (mitochondrial) versus its placement as sister to Gigartinales (plastid). This study demonstrates the need for greater taxon and genomic coverage, including nuclear genes, to better understand relationships among Gigartinales and to support more confident taxonomic decisions regarding Peyssonneliaceae.