MYRTACEAE. Metrosideros robusta: Auckland, Hicks Bay, 100 m, type collection, P.D.D. herbarium, No. 11483.

Hymenophore a tenuous greyish film barely visible upon the substratum, annual, arachnoid, adherent, to 5 x 2 cm; hymenial surface dingy white, delicately pruinose, arachnoid; margin arachnoid, white, adherent. Context a tenuous layer 10-18 µ, thick, basal layer of a few repent hyphae, soon collapsed, intermediate layer wanting; generative hyphae 2-2.5 µ diameter, walls 0.2 µ thick, naked, with clamp connections. Cystidia arising in the base of the context and projecting for the greater part of their length, cylindrical or slightly attenuated towards the rounded and inflated apices, 45-64 x 4-6 µ, bases forked, lumena capillary, save at apices where expanded and bulbous, walls naked or as often enmeshed in delicate hyphal sheaths. Hymenial layer composed of scattered basidia, paraphyses, and cystidia. Basidia clavate, 6-8 x 4-5 µ, bearing 4 spores; sterigmata arcuate, to 4 µ long. Paraphyses clavate, 4-6 x 3-4 µ. Spores globose, apiculate, 3.5-4 µ diameter, walls smooth, hyaline, 0.2 µ thick.

TYPE LOCALITY: Hicks Bay, Auckland, New Zealand.
DISTRIBUTION: New Zealand.

HABITAT: Effused on decayed decorticated fallen trunks.

Cystidia project for almost their entire length, and are cylindrical or slightly tapering with inflated apices; walls, save at apices, are so thickened that lumena are capillary, and are destroyed with aqueous solutions of potassium hydroxide. They become enmeshed in hyphal sheaths. Apices are thin-walled and inflated so that cystidia, like those of T. gracillima, resemble miniature inverted thermometers. Basidia are small, clavate, and develop directly, from hyphae of the basal layer. Fructifications appear as delicate white or greyish arachnoid films upon the surface of fallen decayed trunks; visible to the eye when fresh, in the herbarium fructifications can be seen only with the aid of a dissecting microscope.
The species resembles T. accedens (B. & G.) Donk in shape of the cystidia, but differs in the smaller basidia, globose spores and more delicate fructifications.