P. acuminatus is a small brown mushroom that has black
spores. It has a cap that is less than 4 cm across,
hygrophanous,
conic to campanulate to plane, usually with an
umbo. The
gills are dark purplish black, crowded, with several tiers of intermediate gills. The spores are (11) 13 - 15 (17) x 9 - 11 (12) x (6.5) 7 - 8 (9) micrometers, smooth, black, and shaped like lemons. Cheilocystidia present. == Habitat and distribution ==