An exhaustive survey of vascular epiphytes on a single mature canopy tree in a Costa Rican tropical premontane wet forest revealed an extraordinary level of epiphyte diversity. A total of 126 morphospecies representing at least 52 genera and 21 plant families were found growing epiphytically on the phorophyte (host tree), accounting for more than 1% of the entire vascular flora of Costa Rica. This is considerably higher than most other epiphyte surveys of single trees. Angiosperms accounted for 64% of the species while leptosporangiate ferns accounted for 36%. Consistent with earlier studies, orchids contributed less than would be expected from their global representation, while ferns contributed more significantly to species diversity. Fewer species were found on the tree trunk (58 species) than in the crown (85 species), and little species overlap occurred between these two regions (17 species), suggestive of niche partitioning. Three species and 11 individuals per m 2 were recorded on the trunk of the phorophyte. Our results underscore the important contributions of epiphytes to overall biodiversity, and highlight the necessity of including epiphytes in future biodiversity assessments.