New Zealand: "West coast, Lake Hochstetter; 12.111.1968, leg. Horak (PDD, 27124: holotype; ZT, 68/148: isotype)".

Pileus 10-20 mm diam., hemispherical to convex, margin incurved; dark brown, fuscous; dry, covered at disc with coarse erect or repent conical scales and squamules, which get smaller towards the substriate margin, veil remnants absent. Lamellae adnexed to adnate, ventricose, crowded (L-18, 1-3); pale yellow-brown when young, turning brown, edge concolorous or albo-fimbriate. Stipe 15-35 x 2-3 mm, cylindrical, equal; concolorous with pileus or paler; upper part pruinose, towards base covered with white to yellowish, appressed, longitudinal fibrils from veil; dry, hollow, single and cespitose. Context brown. Odour and taste pleasant, fruity, not distinctive.
Spores 7-8.5 x 4-5 µm, amygdaliform to sublimoniform, brown, smooth. Basidia 22-28 x 6-7 µm, 4-spored. Cheilocystidia clavate to vesiculose, thin-walled, often encrusted with brown pigment. Pleurocystidia 40-60 x 13-20 µm, broadly fusoid, very thick-walled (-8 µm diam.), yellow-brown, crystals present. Caulocystidia -150 x -20 µm, subfusoid-cylindrical, metuloid, encrusted. Cuticle a trichoderm of cylindrical hyphae (4-12 µm diam.), encrusted with yellow-brown pigment. Clamp connections on septae.

On rotten wood and bark of Dacrydium Cupressinum in Nothofagus forest. New Zealand.

Pileo -20 mm lato, hemisphaerico dein convexo, fusco, squamis conspicuis concoloribus obtecto, fibrilloso marginem versus, sicco. Lamellis adnato-adnexis, brunneis. Stipite -35 x -3 mm, cylindrico, pileo concolori, fibrillis albo-luteis basim versus instructo, sicco. Odore nullo. Sporis 7-8.5 x 4-5 µm, amygdaliformibus. Cheilocystidiis clavato-catenulatis. Pleurocystidiis grosse metuloideis. Habitatio ad lignum putridum et aciculos Dacrydii cupressini in silvis nothofagineis. Nova Zeiandia. Typus (PDD, 27124).

In the field I. destruens could be taken as I. umbrosa Hk. because both species show deep brown to fuscous colours on the pileus and the stipe of both taxa is obviously farinaceous. The very thick-walled, rather stout, and yellow-brown pigmented pleurocystidia separate I. destruens well from I. umbrosa, which may occasionally occur on rotten wood and bark.