Third time lucky? Another substantially revised sectional classification for Australasian Plagiochila (Plagiochilaceae: Jungermanniopsida)

Abstract

Molecular phylogeny reconstruction has motivated recircumscription of all families and most genera within the Lophocoleinae, and in Plagiochila, the largest genus of this lineage, has refined the sectional classification as well. Here, we extend this ongoing revision in the first study focusing on species from Australasia, a region to date underrepresented in molecular phylogenetic datasets. We reconstructed a phylogeny containing more than 300 individuals from Australasia and the Pacific, and with this tested sectional circumscriptions within the two largely contradictory classifications recently proposed for Plagiochila. Neither scheme satisfactorily captures relationships among species and all sections prove paraphyletic or polyphyletic, with the exception of those defying these properties by virtue of containing only one species. We propose expanding the circumscription of several sections as the best option for achieving a revised classification representing monophyla that remains stable over the short to medium term, given current knowledge. Broader circumscriptions are proposed for section Denticulatae with section Tayloriae as a new synonym; section Arrectae with section Caducifoliae as a new synonym; a reinstated section Deflexifoliae; and section Plagiochila, to include P. trapezoidea; section Belangerianae to include sections Annotinae, Mitteniae and Strombifoliae as new synonyms; and section Durae with section Colensoae as a new synonym. Section Fragmentissimae is applied to the lineage previously named section Deltoideae nom. inval. or section Hodgsoniae nom. inval., as the Tasmanian P. ratkowskiana and New Zealand P. fragmentissima are the same, and sister to other species in the lineage containing P. deltoidea. Morphological characters supporting these groups are identified, but more importantly the proposed revisions provide a robust framework on which informed re-examination of morphology within this variable and species-rich genus can proceed, and we introduce some encouraging avenues in this area.