Host specificity and low reproductive success in the rare endemic Puerto Rican orchid Lepanthes caritensis

Abstract

Tree host specificity is unusual in orchids. Here we show host specificity in a rare orchid and describe other potential causes of host specificity. Lepanthes caritensis occurs only in Carite State Forest, Puerto Rico. We found L. caritensis only on the largest individuals of one species of tree, Micropholis guyanensis, limiting the orchid to only 7% of the potential tree community > 5 cm dbh. Orchid occurrence was associated with high moss cover on M. guyanensis. The abundance of undescribed fungi cultured from tree bark was negatively associated with orchid presence. Low fruit production in orchids is not uncommon, but reproductive success in L. caritensis appeared to be unusually low; no fruits were produced by 68 adults during 16 months of observation. If this trend of low reproductive success is borne out over time, it would suggest an obvious explanation for the rarity of L. caritensis. Our results suggest ways to manage populations of L. caritensis, but also reveal aspects of tropical orchid biology (e.g. the importance of fungi and mosses for orchid establishment) which require more thorough investigation.