Butyriboletus appendiculatus

Cuticle filamentous, composed of hyphae intricately interwoven with abundant brown intracellular pigment and numerous terminal hyphae very slightly widened with rounded tips, without clamp connections.

Cystidia scattered, of diverse morphology: clavate, pyriform, fusiform or cylindrical.

Basidia clavate and 4-spored.

Spores cylindrical to fusiform, pale yellow under the microscope, thick-walled, with a lateral apiculus and internal oil droplets.