Bitter Scalewort
Porella arboris-vitae
Bitter Scalewort (Porella arboris-vitae) is a leafy liverwort that forms distinctive flattened, scale-like mats on tree bark and rock surfaces. This small bryophyte displays overlapping leaves arranged in three rows, creating a characteristic braided appearance, and plays a crucial role in forest ecosystems by contributing to nutrient cycling and providing microhabitat for invertebrates.
Photo: iNaturalist: (c) Stefan Gey, some rights reserved (CC BY-NC), uploaded by Stefan Gey
Taxonomy & Classification
Kingdom
Plantae
Phylum
Marchantiophyta
Class
Jungermanniopsida
Order
Porellales
Family
Porellaceae
Genus
Porella
Bitter Scalewort belongs to the family Porellaceae, order Porellales, within the Jungermanniopsida class.
Species Profile
Bitter Scalewort (Porella arboris-vitae) is a leafy liverwort that forms distinctive flattened, scale-like mats on tree bark and rock surfaces. This small bryophyte displays overlapping leaves arranged in three rows, creating a characteristic braided appearance, and plays a crucial role in forest ecosystems by contributing to nutrient cycling and providing microhabitat for invertebrates.
Bitter Scalewort (Porella arboris-vitae) is critically endangered primarily due to habitat loss and degradation of old-growth forests where it grows as an epiphyte on ancient trees. The species is extremely sensitive to air pollution, particularly acid rain and atmospheric nitrogen deposition, which alter the chemical composition of tree bark and surrounding environment. Climate change poses an additional threat through altered precipitation patterns and temperature increases that affect the humid microhabitats this bryophyte requires.
Key Facts
Habitat & Distribution
Bitter Scalewort grows exclusively on the bark of mature deciduous trees, particularly favoring the trunks and lower branches of ancient oaks, maples, and ash trees in humid, old-growth forests. It requires stable microclimatic conditions with consistent moisture levels and clean air quality found in undisturbed woodland environments.
Threats
IUCN Red List: Critically Endangered
Bitter Scalewort (Porella arboris-vitae) is critically endangered primarily due to habitat loss and degradation of old-growth forests where it grows as an epiphyte on ancient trees. The species is extremely sensitive to air pollution, particularly acid rain and atmospheric nitrogen deposition, which alter the chemical composition of tree bark and surrounding environment. Climate change poses an additional threat through altered precipitation patterns and temperature increases that affect the humid microhabitats this bryophyte requires.
Air pollution and acid rain
Habitat loss and forest fragmentation
Loss of suitable host trees
Atmospheric nitrogen deposition
Climate change and altered precipitation patterns
National vs Global Threat Status
How this species is assessed at the national level compared to its IUCN global status (CR).
| Country | National Status | Global Status | Comparison |
|---|---|---|---|
| EU | NTNear Threatened | CRCritically Endangered | Lower local risk |
| EU | NTNear Threatened | CRCritically Endangered | Lower local risk |
National Red List data sourced from the National Red List Project (nationalredlist.org, ZSL) and country-specific Red List authorities.
Community Sightings
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Sources & Attribution
How to Cite
IUCN: IUCN (2025). The IUCN Red List of Threatened Species. Version 2025-1. Available at: https://www.iucnredlist.org. doi:10.2305/IUCN.UK.2025-1.RLTS
GBIF: GBIF.org (2025). GBIF Home Page. Available at: https://www.gbif.org
National Red Lists: ZSL (2025). National Red List. Zoological Society of London. Available at: https://www.nationalredlist.org
This page: SpeciesRadar (2025). Bitter Scalewort (Porella arboris-vitae). SpeciesRadar: Intelligence for Earth's Biodiversity. Available at: https://speciesradar.org/species/bitter-scalewort