The Role of the Velamen, Leaves, and Pseudobulbs in Different Species of Costa Rican Orchids
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Epiphytic orchids have been studied for the adaptations they possess to help them deal with xeric conditions particularly when rainfall is low. To help them cope with dehydration, orchids can employ succulent leaves, water storage organs called pseudobulbs, or aerial roots to increase their tolerance. An important feature of the orchid aerial roots is the velamen layer whose purpose is to act like a sponge to passively mediate moisture exchange. The focus of this research was to determine if velamen layer thickness was correlated to water absorption and transpiration rate. The relationship between velamen layer thickness and habitat was studied as predictions were made that orchid roots with a thicker velamen layer were more likely to reside in a more arid forest or higher in the canopy. Likewise, orchids growing in lower altitude or higher moisture conditions would require less velamen cell layers and would not necessarily possess pseudobulbs or thicken leaves. Thirteen different orchid species were collected throughout the OTS biological station La Selva in Costa Rica. Results suggest that velamen cell layer of the aerial root aided in water absorption particular within the initial 10 minutes, however, despite the different velamen thickness in various orchid species, water loss reached its minimum weight after 30 minutes or less.