Pellia is a small but widespread genus of liverworts belonging to the family Pelliaceae in the order Pelliales, class Jungermanniopsida. The genus comprises roughly a dozen accepted species and is found predominantly in cool and temperate regions of the Northern Hemisphere, where it favours moist, shaded habitats such as stream banks, wet rocks, and damp soil.
As liverworts (non-vascular land plants), Pellia species lack true roots, stems, and leaves. They grow as flat, ribbon-like or lobed thallus structures — simple undifferentiated plant bodies — that form dense, bright-green mats, often overlapping one another on wet surfaces. Like all liverworts, they reproduce by spores and display an alternation of generations between a dominant gametophyte phase and a smaller, dependent sporophyte.
The genus is divided into two subgenera: Pellia (subgenus Pellia) and Apopellia (subgenus Apopellia). Notable species include Pellia epiphylla, one of the most common and widely studied liverworts in Europe and North America; Pellia neesiana, which occurs across the Northern Hemisphere; and Pellia undulata, recognised by its distinctly wavy thallus margins.
Pellia liverworts are occasionally encountered in aquarium horticulture, where they are sometimes confused with the aquatic plant marketed as "Süsswassertang" — now established to be the indeterminate gametophyte of a Lomariopsis fern — and with Monosolenium tenerum, another liverwort.
Etymology
The name Pellia was established by the Italian botanist Giovanni Raddi in 1818. The derivation of the name has not been documented in the sources consulted.
Distribution
Pellia is distributed across cool and temperate regions of the Northern Hemisphere, occurring in Europe, Asia, and North America. Individual species show finer geographic ranges: P. epiphylla is broadly widespread in the Northern Hemisphere, while P. neesiana has a subspecies (columbiana) restricted to western North America.
Ecology
Pellia species occupy moist, shaded microhabitats — stream margins, wet cliff faces, damp banks, and woodland floors — where they form spreading thallus mats. They are non-vascular and depend on proximity to water for fertilisation, as their flagellate sperm must swim to reach the egg. The genus is a characteristic indicator of humid, undisturbed riparian and woodland environments in temperate zones.
Taxonomy Notes
Pellia was described by Raddi (1818) and is now placed in the order Pelliales, family Pelliaceae, class Jungermanniopsida. The current species circumscription follows Söderström et al. (2016). The genus is divided into two subgenera: Apopellia Grolle 1983 and Pellia Raddi 1818. The aquarium plant sold as "Süsswassertang" was long misidentified as Pellia endiviifolia (placed in Apopellia) but is now confirmed to be a Lomariopsis fern gametophyte.
