Brook Floater vs Common Tarcrust

Alasmidonta varicosa compared with Diatrype stigma

Key Differences

• Brook Floater is Vulnerable while Common Tarcrust is Not Evaluated.

Taxonomic Classification

Rank	Brook Floater	Common Tarcrust
Kingdom	Animalia (Animals)	Fungi (Fungi)
Phylum	Mollusca (Mollusks)	Ascomycota (Sac Fungi)
Class	Bivalvia (Bivalvia)	Sordariomycetes (Sordariomycetes)
Order	Unionida (Unionida)	Xylariales (Xylariales)
Family	Unionidae	Diatrypaceae
Genus	Alasmidonta	Diatrype
Species	Alasmidonta varicosa	Diatrype stigma

Conservation Status

Brook Floater

VU — Vulnerable

Common Tarcrust

NE — Not Evaluated

Physical Characteristics

Attribute	Brook Floater	Common Tarcrust
Diet	—	—
Average Lifespan	—	—
Average Length	—	—
Average Weight	—	—

Habitat & Geographic Range

Brook Floater

Habitat

Native to North America, inhabiting ecosystems characteristic of the region.

Range

Found in United States. Currently classified as Vulnerable on the IUCN Red List, this species faces significant conservation challenges across its range.

Common Tarcrust

Habitat

Native to Europe, inhabiting ecosystems characteristic of the region.

Range

Distributed across Belgium, Denmark, Norway, Portugal, and Sweden.

Brook Floater

The Brook Floater (Alasmidonta varicosa) is a species in the genus Alasmidonta. It is currently classified as Vulnerable on the IUCN Red List. Native to North America, inhabiting ecosystems characteristic of the region.

Common Tarcrust

<em>Diatrype stigma</em>, the common tarcrust, is a saprotrophic fungus in the family Diatrypaceae, found across Belgium, Denmark, Norway, Portugal, and Sweden, as well as more broadly in Europe and temperate regions globally. It grows as a crust-like, charcoal-black stromata on the dead bark and branches of deciduous hardwoods, particularly hazel, beech, and alder. The fruiting bodies are typically flat to slightly raised, dark gray to black patches that contain numerous embedded perithecia in which ascospores are produced. This fungus plays an important ecological role as a decomposer, breaking down dead woody material and recycling nutrients in forest ecosystems. It is Not Evaluated on the IUCN Red List; given its broad distribution on common substrates, it is generally considered widespread. The species reproduces via wind-dispersed ascospores released from the perithecia. Diet, as a saprotrophic organism, consists of dead organic woody matter. Biological traits such as colony growth rates, spore output, and longevity remain poorly documented in standardized quantitative assessments.