The holotype was collected in Øvre Dividal National Park, in Målselv Municipality (Norway), where it was growing on Salix.
The fungus has a monomitic hyphal system, with individual hyphae measuring 2.5–4 μm and having a clamp connection and oily refractive contents.
The basidia are four-sterigmate, measure 30–50 by 8 μm, and feature a hook-shaped protuberance.
Its spores are ellipsoid to obovate in shape, measuring 9 by 6 μm.
[1] Uncobasidium roseocremeum, found in South America, differs microscopically from U. luteolum in its larger, spherical spores, and the presence of encrusted hyphidia.