BRIEF DESCRIPTION: The original description (Corner & Bas, 1962) is the source of the following.  The cap of A. xanthomargaros is fuscous-brown to olivaceous brown, fuscous over the disc, yellowish near the margin, with innate, dark, radiating fibrils, 45 mm wide, plano-convex, dry, with a nonstriate margin.  The cap is decorated with numerous, friable, soft, conical, umber-brown warts with yellow tips.

The gills are free, crowded, and white.

The stem is 55 x 3 - 8 mm, attenuate upward, solid, pale grayish brown, and yellowish at the apex.  The flesh is white, becoming pale brownish or grayish-brownish on cutting, especially in the stem.

Spores from dried material measure 5.4 - 6.4 x 4.4 - 5.3 µm (from fresh material, 6 - 7 x 5 - 6 µm wide) and are subglobose to broadly ellipsoid and amyloid.  Clamps were not observed at the bases of basidia.

This species was described from Singapore.  For comparison, see A. pausiaca Corner & Bas.  Small taxa in sect. Validae with friable yellow volvas are listed for purposes of comparison under A. flavoconia G. F. Atk. var. flavoconia. -- R. E. Tulloss