Apopellia is a small genus of thallose liverworts in the family Pelliaceae (order Pelliales, class Jungermanniopsida, phylum Marchantiophyta). It was formally recognized at genus rank by Nebel & D.Quandt in 2016 (published in Taxon 65(2): 230), having previously been treated as subgenus Apopellia Grolle within the broader genus Pellia. The genus comprises up to three species — A. endiviifolia, A. alpicola, and A. megaspora — of which A. endiviifolia is by far the most widespread and commonly encountered.
Members of Apopellia are thallose liverworts, meaning the plant body is an undivided, ribbon-like or strap-shaped green thallus rather than the leafy shoots seen in some other liverwort groups. As members of Pelliaceae, they are visibly distinct from the leafy liverwort families and lack the dorsal midrib seen in some related genera. The thallus lacks a clearly defined midrib or internal differentiation, lying flat and often branching dichotomously.
Apopellia endiviifolia is widely distributed across cool and temperate regions of the Northern Hemisphere, with occurrence records spanning western Europe (especially the British Isles, France, the Benelux countries, Scandinavia, and Germany), eastward through Russia, and into Japan and parts of North America. It grows in moist, shaded habitats — stream banks, wet rocks, damp soil, and cave entrances — where it can form dense, bright-green mats.
The genus is of some interest to aquarium hobbyists: A. endiviifolia (under its former name Pellia endiviifolia) was commonly sold as an aquatic plant. However, the submerged form known as "Süsswassertang" that was long traded under this name proved to be the indeterminate gametophyte of a Lomariopsis fern rather than a true liverwort.
Etymology
The name Apopellia derives from the subgenus Apopellia Grolle, which was elevated to genus rank by Nebel & D.Quandt in 2016. The prefix apo- (from Greek, meaning "away from" or "separate") signals its segregation from the parent genus Pellia Raddi. The genus name Pellia itself was coined by Giovanni Battista Raddi in 1818.
Distribution
Apopellia endiviifolia, the most widespread species in the genus, occurs across cool and temperate regions of the Northern Hemisphere. Occurrence records are concentrated in western Europe — particularly the British Isles, France, Belgium, the Netherlands, Sweden, Ireland, and Germany — with additional records from Switzerland, Spain, Poland, Russia, Japan, and North America.
Ecology
Members of Apopellia are found in moist, shaded environments, typically growing on stream banks, wet rock faces, damp soil, and the entrances of caves, where they form dense bright-green mats of thallose tissue. Like other Pelliaceae, they favour cool, humid conditions in temperate to boreal climates.
Taxonomy Notes
Apopellia was elevated from subgenus to genus rank by Nebel & D.Quandt in 2016 (Taxon 65(2): 230), based on molecular and morphological work by Schütz, Quandt & Nebel (2016, Taxon 65(2): 221–234). The basionym is Pellia subgen. Apopellia Grolle. Wikispecies recognizes three species (A. endiviifolia, A. alpicola, A. megaspora); GBIF currently lists one accepted descendant, reflecting incomplete uptake of the 2016 reclassification. The type species is A. endiviifolia (Dicks.) Nebel & D.Quandt, formerly Pellia endiviifolia (Dicks.) Dumort.
