Hydraulics link leaf shape and environmental niche in terrestrial bromeliads

Terrestrial species of the megadiverse bromeliad family display a wide variety of leaf shapes, many of which have evolved convergently in different lineages. Here, I examine the links between leaf shape, venation architecture, hydraulic function, and bioclimatic relations in two bromeliad groups displaying diverse leaf shapes, the genus Pitcairnia (Pitcairnioideae) and the terrestrial grade of the Bromelioideae subfamily. Leaf shapes with broader leaf blades, notably petiolate and lanceolate morphologies, tend to show wider vein spacing, which is associated with reduced hydraulic capacity and higher hydraulic vulnerability. In turn, these leaf shapes tend to occur in species restricted to moist, aseasonal environments, suggesting that hydraulic function is an important mediator of the relationship between leaf shape and bromeliad environmental niches. This network of trait-trait and trait-environment relationships may have been of profound important in the ecological and evolutionary diversification of the bromeliads. Similar structure-function principles are likely to apply in other tropical herbaceous monocots, which are of great ecological importance but generally neglected in plant hydraulic research.