Fracture of the dimorphic fruits of Aethionema arabicum (Brassicaceae)

Abstract

Fruits exhibit highly diversified morphology, and are arguably one of the most highly specialised organs to have evolved in higher plants. Fruits range in morphological, biomechanical, and textural properties, often as adaptations for their respective dispersal strategy. While most plant species possess monomorphic (of a single type) fruit and seeds, here we focus on Aethionema arabicum (L.) Andrz. ex DC. (Brassicaceae). Its production of two distinct fruit (dehiscent and indehiscent) and seed types on the same individual plant provides a unique model system with which to study structural and functional aspects of dimorphism. Using comparative analyses of fruit fracture biomechanics, fracture surface morphology, and internal fruit anatomy, we reveal that the dimorphic fruits of A. arabicum exhibit clear material, morpho-anatomical, and adaptive properties underlying their fracture behaviour. A separation layer along the valve–replum boundary is present in dehiscent fruit, whereas indehiscent fruit have numerous fibres with spiral thickening, linking their winged valves at the adaxial surface. Our study evaluates the biomechanics underlying fruit-opening mechanisms in a heteromorphic plant species. Elucidating dimorphic traits aids our understanding of adaptive biomechanical morphologies that function as a bet-hedging strategy in the context of seed and fruit dispersal within spatially and temporally stochastic environments.