Exidia zelleri is a species of fungus in the family Auriculariaceae. Basidiocarps (fruit bodies) are gelatinous, pale violaceous grey to grey-brown, button-shaped at first then coalescing and becoming irregularly effused. It grows on dead branches of broadleaved trees and is known from north-western North America.
The species was first described in 1920 from Oregon by mycologist Curtis Gates Lloyd.
The basidiocarps of E. zelleri are gelatinous, button-shaped to top-shaped and attached to the wood at a point, sometimes coalescing to form effused, irregular masses up to 8 cm across. pale violaceous grey to grey brown, darkening with age. The surface is sparsely to densely covered in small papillae (pimples).
The translucent hyphae are thin-walled and form clamp connections. Basidia are elliptical and consist of four longitudinally septate cells. Basidiospores are allantoid (sausage shaped), 16 to 19 by 5 to 6 μm, with thin, smooth walls.
Fruit bodies of Exidia crenata and Exidia recisa also occur on broadleaved trees in North America, but are typically reddish to orange-brown and lack papillae on the surface. Exidia glandulosa has papillae, but is typically blackish brown to black.
Exidia zelleri was originally described from Oregon and has also been recorded from California and British Columbia. It was originally collected on dead wood of Sambucus, but has subsequently been reported on other broadleaved trees.