Speckled Tar Spot

Speckled Tar Spot is a parasitic fungus infecting several species of maple (Acer). In Minnesota it infects only mountain maple and silver maple.

It appears as a more or less round, about ½″ in diameter, yellowish-green spot with a dense cluster of numerous tiny, raised black specks.

In the fall a ring of green will be seen around areas infected by the fungus as the remainder of the leaf fades. The green areas remain photosynthetic.

Black Tar Spot (Rhytisma acerinum) causes large solid black spots up to 1½″ in diameter.

Mountain maple and silver maple

Spring to fall

Sources

7, 26, 29, 30, 77.

Biodiversity occurrence data published by: Minnesota Biodiversity Atlas (accessed through the Minnesota Biodiversity Atlas Portal, bellatlas.umn.edu, 7/24/2025).

Common and widespread

The life cycle of this and most other fungi is pleomorphic. It has both an asexual reproductive phase (anamorph) and a sexual reproductive phase (telemorph). Each phase is often morphologically distinct. In the past, the International Code of Botanical Nomenclature allowed each phase to be assigned a different scientific name. It was incorrect to refer to the anamorph phase by the telemorph name, and vice versa. Some mycologists and molecular biologists consider this practice to be obsolete. Molecular phylogeny allows the accurate placement of a species in any part of their life cycle. On July 30, 2011, at the meeting of the XVIIIth International Botanical Congress in Melbourne, Australia, that practice ended. Prior to that meeting, the early, anamorphic phase of this fungi had been named Melasmia punctata. Both phases are now named Rhytisma punctatum.

Rhytisma punctatum - fungi kingdom
Nineli Lishina