Are tropical fungal endophytes hyperdiverse?

Fungal endophytes are ubiquitous fungi that inhabit healthy plant tissues w ithout causing disease. Endophytes have been found in every plant species e xamined to date and may be important, but often overlooked, components of f ungal biodiversity. In two sites in a lowland, moist tropical forest of cen tral Panama, we quantified endophyte colonization patterns, richness, host preference, and spatial variation in healthy leaves of two co-occurring, un derstory tree species [Heisteria concinna (Olacaceae) and Ouratea lucens (O chnaceae)]. From 83 leaves, all of which were colonized by endophytes, we i solated 418 endophyte morphospecies (estimated 347 genetically distinct tax a), most of which were represented by only a single isolate (59%). Among mo rphospecies encountered in more than one leaf (nonsingletons), we found evi dence of host preference and spatial heterogeneity using both morphospecies frequencies and presence/absence records. Based on these data, we postulat e that tropical endophytes themselves may be hyperdiverse and suggest that extrapolative estimates that exclude them will markedly underestimate funga l species diversity.