Plagiochila is a large and widespread genus of leafy liverworts (division Marchantiophyta) belonging to the family Plagiochilaceae within the order Jungermanniales. It is one of the largest genera of liverworts, with estimates of accepted species ranging from 500 to 1,300, the wide range reflecting ongoing taxonomic revision and the discovery that many morphologically distinct populations may represent recent diversification events rather than long-isolated lineages.
The genus has a cosmopolitan distribution, found on every continent except Antarctica. The majority of species occur in tropical regions, particularly in humid montane forests. In Britain and Ireland, nine species are recorded, most with a hyper-oceanic distribution that requires the high atmospheric humidity found near the Atlantic coast. Plagiochila spinulosa is the most widespread of these oceanic species, characteristic of Atlantic temperate rainforests, and also maintains a disjunct population in New Zealand.
Plagiochila taxonomy is actively debated. Molecular phylogenetic studies have revealed weak genetic boundaries between many observed species, consistent with recent and rapid diversification. European species have in some analyses been found to be conspecific with, or closely related to, tropical American taxa, while remaining genetically distinct from Asian representatives, complicating traditional morphology-based classifications.
Distribution
Plagiochila has a cosmopolitan distribution, recorded on every continent except Antarctica, with the greatest diversity of species in tropical regions. In Britain and Ireland, nine species occur, most of them hyper-oceanic and dependent on Atlantic humidity; Plagiochila spinulosa is the most widespread, growing in Atlantic temperate rainforests and with a disjunct population in New Zealand.
Taxonomy Notes
Plagiochila taxonomy is complex and contested. Phylogenetic analyses have revealed weak genetic differentiation among many species, suggesting recent diversification rather than ancient divergence. European taxa have been treated as conspecific with, or closely related to, tropical American species, while Asian species appear more genetically distinct. The genus was established by Dumortier (Dumort.) Dumort., 1835, and the total number of accepted species remains under active revision, with estimates spanning 500 to 1,300.
