This key to Clitopilus was written by Timothy J. Baroni (SUNY Cortland, Cortland, New York, USA) and appeared in Brittonia 52: 121-135. 2000.
Vouchers for all collections are on deposit in the mycological herbaria at the Universidad de Costa Rica (USJ) or Instituto Nacional de Biodiversidad (INB). Duplicates are in the Field Museum (F), SUNY Cortland (CORT), or the New York Botanical Garden (NY).
1. Basidiomata clitocyboid; pileus 2-5 cm broad; spores typically with (5-)6(-7 longitudinal ridges . . . Clitopilus griseobrunneus Baroni & Halling
1. Basidiomata pleurotoid; pileus typically less than 1 cm broad, dimidiate or conchate; spores typcially with 8-10(-11) longitudinal ridges . . . 2
2. Pileus and lamellae reddish or brownish red; context with abundant amorphous intercellular pigment bodies, these tissues becoming bright pink in 50% HCl mounts . . . Clitopilus rhodotrama Singer
2. Pileus white or grayish brown; lamellae white or pale creamy, becoming pale pinkish with spore maturation; context lacking intercellular pigment bodies and the tissues remaining hyaline in 50% HCl mounts . . . 3
3. Pileus grayish brown, often sulcate; dark brown plate-like incrustations present on hyphae of the pileipellis . . . Clitopilus incrustatus var. incrustatus Singer
3. Pileus white or sordid whitish, typically not sulcate; lacking incrustations on the hyphae of the pileipellis . . . 4
4. With obvious, long projecting, filiform cheilocystidia . . . Clitopilus hobsonii var. cystidiosus Baroni & Halling
4. Lacking obvious, long projecting, filiform cheilocystidia . . . Clitopilus hobsonii var. hobsonii