Definitions

1. noun

A fungus causing black spots to form on tree bark, especially oak, producing small black fruiting bodies.

“The rhytisma fungus causes unsightly black spots on the oak tree’s bark, but it’s harmless.”

2. noun

A type of fungus that grows on plants, especially trees, forming black or dark-colored spots or growths.

“Rhytisma fungi are common on oak trees, especially in forests with rich soil.”