BRIEF DESCRIPTION: Fruiting bodies of A. innatifibrilla are small.  The cap is 25 - 45 mm wide, convex to applanate to concave, dark grey-brown to fuligineous over the center, becoming paler towards the margin.  It appears innately radially fibrillose and is covered with verrucose to felty volval remnants that are whitish on their upper parts and grayish to brownish on their lower parts.  The cap's margin is smooth and non-appendiculate, and the context is white.

The gills are free, crowded, and white; the short gills are attenuate.

The stipe is 40 - 60 x 4 - 6 mm, subcylindric or attenuate upwards, with a surface that is whitish to greyish.  The stipe's basal bulb is 6 - 10 mm wide, nearly fusiform, and has its upper part covered with grayish to brownish verrucose, floccose to farinose volval remnants.  The stipe bears a ring that is membranous, with an upper surface that s whitish and a lower surface that is greyish.

The spores of this species measure 6.5 - 8.0 (-9.5) x 5.5 - 7.0 (-7.5) µm and are subglobose to broadly ellipsoid and amyloid.  Clamps are not present at the bases of basidia.