Hymenophore annual, membranous, adnate, effused forming irregular areas to 7 x 4 cm; surface white or ivory white, even, not creviced; margin thinning out, arachnoid, white, adnate. Context white, 60-100 µ thick, basal layer scanty, of parallel hyphae; intermediate layer of loosely arranged ascending hyphae branched at a wide angle, corymbose in the subhymenium; generative hyphae 3-4 µ diameter, walls 0.25 µ thick, hyaline, naked, branched, septate, with conspicuous clamp connexions. Hymenial layer to 25 µ deep, a scanty and irregular palisade of basidia, paraphyses and cystidia. Basidia subclavate, 16-20 x 4-5 µ, 4-spored; sterigmata slender, arcuate, 6-8 µ long. Paraphyses scanty, subclavate, or cylindrical, shorter than the basidia. Cystidia arising from hyphae of the intermediate and basal layers, projecting to 60 µ, aculeate with long-acuminate apices, 64-105 x 5-7 µ, coated save at apices with scanty flattened crystals, walls hyaline, 0.5-1 µ thick, thinning towards apices. Spores elliptical when flattened on one side, or suballantoid, 7-9 x 4-5 µ, walls smooth, hyaline, 0.1 µ thick.

DISTRIBUTION. New Zealand.

HABITAT. Effused on dead leaf midribs.

Hymenophorum annuum, membranaceum, adnatum, effusum; superficie alba, aequa, non rimosa. Hyphae contextus fibulatae, 3-4 µ diam., nudae. Basidia subclavata, 16-20 x 4-5 µ, 4 sporis. Cystidia aculeata, eminentia, 64-105 x 5-7 µ, crystallis sparsis verrucosis tecta. Sporae elliptical vel suballantoides, 7-9 x 4-5 µ, laeves, hyalinae.

P. sororia and P. longispora show a close resemblance in structure of the context and especially the form of the cystidia. The latter are aculeate, taper from base to apex, project for about half their length, are relatively thin-walled, and bear small tuberculate scattered crystals often arranged like plates or scales. P. sororia is separated by its differently shaped shorter spores, and more delicate cystidia being, as its name implies, a little sister of the more robust P. longispora.

Rhopalostylis sapida (Sol.) Wendl. & Drude. Auckland: Cascades, Waitakeres, 900ft, April, 1954, S.D. Baker, type collection, P.D.D.herbarium, No. 13816.