The contact separation force of the fruit burrs from five plant taxa dispersing by epizoochory

Abstract

Many plant diaspores dispersing by epizoochory bear special structures, such as burrs with hooks, which are responsible for the mechanical interlocking with animal fur or feathers. The number, dimensions and distribution of the interlocking structures on the diaspore can strongly vary depending on the plant species. In this study, to evaluate the interlocking ability of distantly related plants having different diaspore morphologies, the contact separation force (CSF) of single burrs was measured in Arctium lappa, Bidens tripartita, Desmodium sp., Uncinia uncinata and Xanthium strumarium. This force is required to separate the single burr from interlocking with the loop. Usually in the experiment, the burr was broken after separation. The CSFs differed significantly, ranging from 7.07 to 820.94 mN, among the five taxa studied. Six morphometrical variables were measured from each burr and the correlations between the CSFs and these morphometrical variables were analyzed. We have shown that (1) the burr length, (2) the diameter of the distal part and (3) the hook span had significant influences on the CSF. The comparison between the CSF and the fruit weight indicated that single burrs of all taxa studied could bear at least 100-fold weight of the diaspore.