Aspects of Orchidaceae distribution in Costa Rica and northwestern South America: a study on similarity with emphasis on the Amazonian Region

Distribuição de Orchidaceae na Costa Rica e Noroeste da América do Sul: um estudo de similaridade com ênfase na Região Amazônica

The purpose of this study was to compare the floristic composition of Orchidaceae among different areas of Costa Rica and northwestern South America, aiming to answer the following questions: 1) Is the variation in the species composition among the study areas better explained by physical features, geographical closeness, or potential endemism centers? 2) Does the floristic similarity decay with geographical distance? We selected 11 surveys conducted in South America and two in Central America (Costa Rica). Cluster analysis was conducted using the software MVSP. The result was a split pattern between Amazonian and non‑Amazonian floristic compositions. The environmental conditions analyzed appear to be important factors in explaining the orchid composition of areas outside the Amazon basin. The Amazonian group is environmentally very uniform, but floristically very distinct, and no physical features were determinant of the internal segregation into two subgroups. Geographic closeness has no influence on the species composition of the areas, and historical factors may explain the pattern observed.

Biogeography; Brazil; Colombia; Costa Rica; Neotropics; Venezuela