Wall Scalewort

Porella platyphylla is a species of liverwort belonging to the family Porellaceae. It has a Holarctic distribution, occurring across Eurasia and North America, where it typically grows on tree bark and rocks in areas with adequate rainfall. The species is most common in regions receiving at least 600 millimetres of annual precipitation. The species forms part of a complex taxonomic group that includes several closely related species and hybrids, with populations showing distinct genetic differences between continents despite their morphological similarity.

The species is characterised by its obtuse-rounded leaf lobes with flat margins, and irregular teeth at the perianth mouth when mature. It reproduces both sexually, with separate male and female plants, and asexually through leaf fragments. P. platyphylla is known for its ability to survive long periods of desiccation, being able to recover normal photosynthetic function within hours of rehydration. The species produces unique chemical compounds, including pinguisane sesquiterpenoids and sacculatane diterpenoids, which help distinguish it from related species. Recent molecular studies have revealed significant genetic variation within the species, particularly in European populations, though this variation is not always reflected in physical characteristics.