A tropical epiphytic orchid uses a low‐light interception strategy in a spatially heterogeneous light environment

Light is considered a non‐limiting factor for vascular epiphytes. Nevertheless, an epiphyte's access to light may be limited by phorophyte shading and the spatio‐temporal environmental patchiness characteristic of epiphytic habitats. We assessed the extent to which potential light interception in Rodriguezia granadensis, an epiphytic orchid, is determined by individual factors (plant size traits and leaf traits), or environmental heterogeneity (light patchiness) within the crown of the phorophyte, or both. We studied 104 adult plants growing on Psidium guajava trees in two habitats with contrasting canopy cover: a dry tropical forest edge, and isolated trees in a pasture. We recorded the number of leaves and the leaf area, the leaf position angles, and the potential exposure of the leaf surface to direct irradiance (silhouette area of the leaf blade), and the potential irradiance incident on each plant. We found the epiphytes experience a highly heterogeneous light environment in the crowns of P. guajava. Nonetheless, R. granadensis plants displayed a common light interception strategy typical of low‐light environments, resembling terrestrial, forest understory plants. Potential exposure of the total leaf surface to direct irradiance correlated positively with plant size and within‐plant variation in leaf orientation. In many‐leaved individuals, within‐plant variation in leaf angles produced complementary leaf positions that enhanced potential light interception. This light interception strategy suggests that, in contrast to current wisdom, enhancing light capture is important for vascular epiphytes in canopies with high spatio‐temporal heterogeneity in light environments.