<p>Upper Andean tropical forests represent a unique biodiversity region with distinctive floristic composition. However, our understanding of functional trait variation, its differences between growth forms, and the relationships between traits remains limited in this region. This study aimed to analyse the variation in leaf anatomical traits in upper Andean tropical forests of Colombia, compare differences between trees and shrubs, and examine trait correlations. Leaf anatomical traits from 38 tree species and 25 shrub species were obtained from 189 individuals. Measured traits included cuticles, epidermis, hypodermis, palisade and spongy mesophylls, vascular bundles, and air spaces. Significant differences in all anatomical traits were found between species, highlighting the wide variety of tissue combinations in shapes and sizes. On average, trees exhibited thicker protective tissues than shrubs, but only the percentage of adaxial cuticle thickness was statistically significant. These minimal differences are likely due to limited vertical stratification, lower canopy height and reduced aboveground biomass, which decrease the selection pressure for shade-tolerant species with thicker leaf anatomical traits. Potential trade-offs were identified within mesophyll tissues (an inverse relationship between palisade and spongy tissues), between photosynthetic efficiency and leaf protection (an inverse relationship between the palisade/spongy ratio and the adaxial cuticle/abaxial cuticle ratio), and between cell aspect ratios of epidermis and mesophyll tissues (an inverse relationship between the aspect ratio of epidermis cells and that of palisade and spongy cells). This is the first study that analyses the leaf anatomical basis underlying the life-history strategies of trees and shrubs in Andean montane forests and the potential trade-offs involved.</p>