Coccomyces dentatus

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Coccomyces dentatus is a common saprobic fungus in the Rhytismataceae family. It lives on dead fallen leaves of flowering plants, especially oaks and chestnuts, in warm, temperate regions.

What it looks like
- In the leaf’s epidermal layer, it forms dark hexagonal apothecia that create a light-to-dark mosaic pattern bounded by thin black lines (zone lines).
- The apothecia are black and shiny, with a star-shaped pattern of grooves, and they open with small triangular flaps to release spores.
- Often pycnidia (asexual fruiting bodies) appear with the apothecia.
- The fungus has an anamorph (asexual form) called Tricladiopsis flagelliformis, known for whip-like conidia.

Taxonomy and naming history
- First described in 1817 as Phacidium dentatum, it was later moved to Lophodermium and then to Coccomyces in 1877, where it currently resides.
- Various forms and related names have been proposed, but some are considered synonyms or of unclear status.

Similar species
- C. dentatus can resemble Coccomyces coronatus, C. tumidus, C. australis, and C. kinabaluensis. They differ in features of the apothecia and microscopic details, so careful examination is needed to tell them apart.

Ecology and distribution
- It is saprobic, growing on dead leaves of many angiosperms. It commonly appears on heath family and beech family leaves, including oaks and chestnuts, and can also be found on Castanea sativa in Chile.
- Other hosts include leaves from Rhododendron, Lithocarpus, Berberis, Arbutus, Gaultheria, and Myrica.
- The species is widespread in warm temperate zones and has been found in Africa (Tunisia), Europe, and the Americas.
- In cooler parts of its range, it appears mainly in summer and autumn; in subtropical areas, it can be found year-round.

Why it matters
- Coccomyces dentatus is very common and conspicuous, making it one of the most frequently collected Coccomyces species.