Seed Morphology of Three Neotropical Orchid Species of the Lycaste Genus

Abstract

Neotropical orchids are vulnerable to extinction due to overharvesting, habitat destruction and climate change. However, a basic understanding of orchid seed biology to support conservation efforts is still lacking for most species. Seed morphology is linked to plant adaptation and evolution, influencing seed dispersal, dormancy, longevity, and germination, which are valuable traits for conservation. In this study, we characterized and compared the morphological traits of seed capsules (size, shape, and colour) and seeds (seed and embryo shape and size and internal airspace volume) for three epiphytic Neotropical orchid species of the genus Lycaste native to Guatemala: L. cochleata, L. lasioglossa, and L. virginalis. The three species show qualitative similarities in seed capsule colour and appearance and in seed morphology (i.e., scobiform oval-shaped seeds and prolate-spheroid embryos). All species have small-sized seeds (length of L. cochleata: 210 µm, L. lasioglossa: 230 µm, and L. virginalis: 260 µm), with proportionally large embryos (length of L. cochleata: 140 µm, L. lasioglossa: 120 µm, and L. virginalis: 150 µm) and an internal air-space volume that occupies less than half of the seed (L. cochleata: 17%, L. lasioglossa: 42%, and L. virginalis: 30%). This finding is consistent with previous reports for other epiphytic orchid species, which typically have lower air volumes than terrestrial orchids. These differences are likely a result of evolutionary changes associated with different habits and may influence seed dispersal. We also found some significant differences in seed morphology between the studied species, but their taxonomic, biological, and ecological relevance remain to be elucidated. More comparative studies, including on other Lycaste species with different habits, are needed to explore relationships between seed morphology, taxonomy, biology, and ecology in this genus to support its conservation.