Diaspore Size, Shape, and Fall Behavior in Wind-Dispersed Plant Species

Abstract

Seeds and fruit of 38 anemochorous species were dropped in still air to simulate their descent under natural conditions. Fall rate and lateral distance were recorded as indices of wind-borne dispersal capability. Differences in fall rates among plumed species were dependent on interspecific variation in diaspore weight and plume area, while fall rates of winged species were strongly differentiated by contrasting wing shapes. In Acer platanoides and Asclepias syriaca, representing wing and plume architectures, respectively, the range of diaspore weight was artificially extended by removing embryos or adding lead weights. In both of these species, rate of descent of altered diaspores was controlled by weight relative to wing or plume area. The wing morphology of A. platanoides showed lower fall rates than the plumed A. syriaca above 45 mg, while the plume morphology of A. syriaca achieved lower fall rates below this weight. Compared with wide variation in diaspore weight, members of the Compositae showed relatively low variation in plume loading (diaspore weight/plume area) and fall speed. These observations suggest functional and phyletic constraints on diaspore architecture. Such constraints may limit evolutionary change in diaspore size and performance.