We studied the occurrence of epiphytic pteridophytes on the trunks of two kinds of hosts: tree ferns and angiosperms. The study was carried out in Costa Rica at the La Selva Biological Field Station (50 m), Las Cruces Biological Field Station (1200 m), Monteverde Cloud Forest Reserve (1500 m), and Cuerici Biological Field Station (2600 m). At each site 20 tree fern trunks with a root mantle were sampled for epiphytes up to a height of 3 meters, and the same was done for the nearest angiosperm trunk of similar diameter at breast height. A total of 106 species of epiphytic pteridophytes were found at all of the study sites, 29 of them occurred frequently enough to test statistically. None of the 29 species occurred more frequently on angiosperm trunks, but 12 occurred more frequently on tree ferns. Seven of these were entirely restricted to tree ferns, whereas the other five also occurred on angiosperm trunks. Tree ferns had a significantly higher number of epiphytic species than angiosperms, averaging (depending on the site) three to five species, whereas angiosperms averaged one or two. Epiphytic pteridophytes were more abundant on the root mantles of tree fern trunks than on the trunks of angiosperms. Species composition of epiphytes was not contingent upon the species of host tree fern. No correlation existed between the species richness and abundance of fern epiphytes and dbh, on neither tree ferns nor angiosperms. In conclusion, fern epiphytes exhibited significant differences in species composition, number of species per trunk, and abundance, on tree fern versus angiosperm trunks. These differences are probably because the root mantles provide more favorable microhabitats for the establishment of fern prothalli and a better substrate for the attachment of fern sporophytes.

Key words: Costa Rica, epiphytes, ferns, pteridophytes, tree ferns