Armillaria umbrinobrunnea is a species of mushroom

Mushroom

A mushroom is the fleshy, spore-bearing fruiting body of a fungus, typically produced above ground on soil or on its food source. The standard for the name "mushroom" is the cultivated white button mushroom, Agaricus bisporus; hence the word "mushroom" is most often applied to those fungi that...

 in the Physalacriaceae

Physalacriaceae

Physalacriaceae are a family of fungi in the order Agaricales. Species in the genus have a widespread distribution, but most are found in the tropics, particularly in South-East Asia and Australasia. Molecular studies suggested that Physalacria, formerly the sole genus in this family, is related to...

 family. This species is found in South America. The beige to light brown caps

Pileus (mycology)

The pileus is the technical name for the cap, or cap-like part, of a basidiocarp or ascocarp that supports a spore-bearing surface, the hymenium. The hymenium may consist of lamellae, tubes, or teeth, on the underside of the pileus...

 of the mushroom are between 15 and 50 mm (0.590551181102362 and 2 in) in diameter, and densely covered in small scales. The species was originally collected in 1952 by Rolf Singer

Rolf Singer

Rolf Singer was a German-born mycologist and one of the most important taxonomists of gilled mushrooms in the 20th century....

 in Argentina, and named as the variety Armillariella montagnei var. umbrinobrunnea.