The Two Cryptic Species of Trema micrantha of Barro Colorado Island

Trema micranthaha (L.) Blume, a light-demanding pioneer tree widely distributed in the Americas, includes four clades, two of which are present in the Barro Colorado Nature Monument (BCNM). Brown Trema, which has a brown seed endocarp, occurs mainly on landslides where mineral soil is exposed, and black Trema, which has a black endocarp, is found mainly in large treefall gaps in the interior of the forest. In addition to genetic differences, these cryptic species, with long-lasting seeds that remain in soil seed banks, contrast in seed dormancy and germination requirements, seed defenses, and seed-associated fungal communities that affect seed survival and germination. Moreover, field and greenhouse studies have shown that differences in soil abiotic (soil nutrients) and biotic (soil microbes) conditions, as well as herbivores, determine habitat segregation of these species. Thus, phylogenetic and ecological data are key to improving our understanding of how abiotic and biotic habitat variation mediate differentiation among tropical cryptic species.