Black Tar Spot
Rhytisma acerinum
Because Rhytisma acerinum is exceptionally sensitive to sulfur dioxide pollution, its presence is widely used as a biological indicator of clean air.
- Scientific name
- Rhytisma acerinum
- Taxonomy
- Fungi › Ascomycota › Leotiomycetes › Rhytismatales › Rhytismataceae › Rhytisma
- IUCN Red List status
- Least Concern
- Population trend
- stable
- Biome
- forest
- Habitat
- Temperate deciduous and mixed forests, parks, and hedgerows with maple trees
- Diet
- Biotrophic parasite on living maple leaves, becoming saprotrophic on fallen leaf litter
- Range
- Europe, North America
- Size
- Individual stromatic spots measure 1–2 cm across
- Lifespan
- 1 yr
- Active
- diurnal
- Threats
- High concentrations of atmospheric sulfur dioxide and urban leaf clearing practices
- Safe to approach?
- Harmless to humans. It does not bite, sting, or produce contact toxins. Maple leaves infected with tar spot can be touched safely, though general hand washing after handling plant debris is good hygiene.
Rhytisma acerinum is a plant pathogen that commonly affects sycamores and maples in late summer and autumn, causing tar spot . Tar spot does not usually have an adverse effect on the trees' long-term health. R. acerinum is an Ascomycete fungus that locally infects the leaves of trees and is a biotrophic parasite. The disease is cosmetic and is therefore usually controlled only with sanitation methods.
Photo: Manuel R Popp, CC-BY, via iNaturalist
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