ABSTRACT Root morphology is expected to respond to environmental conditions. Two earlier studies reported predictable changes in the structure of the velamen radicum (common in monocotyledons) along rainfall gradients, which was expected from its assumed role in plant-water-relations. The present study expanded on this idea by analysing nine root traits that can be linked to root function, including velamen structure, along two moisture gradients of different spatial scales: 1) along the vertical gradient of a lowland forest in central Panama and 2) along a strong regional rainfall gradient in western Panama. All studied traits (e.g. velamen width, number of xylem poles, lignification of the exodermis) of the 45 orchid species showed substantial... |