Comparative Analyses of the Self-Sealing Mechanisms in Leaves ofDelosperma cooperiandDelosperma ecklonis(Aizoaceae)

Within the Aizoaceae, the genusDelospermaexhibits a vast diversification colonizing various ecological niches in South-Africa and showing evolutionary adaptations to dry habitats that might include rapid self-sealing. Leaves ofDelospermareact to external damage by the bending or contraction of the entire leaf until wound edges are brought into contact. A study of leaf morphology and anatomy, biomechanics of entire leaves and individual tissues and self-sealing kinematics after a ring incision under low and high relative humidity (RH) was carried out comparing the closely related speciesDelosperma cooperiandDelosperma ecklonis, which are indigenous to semi-arid highlands and regions with an oceanic climate, respectively. For both species, the absolute contractions of the examined leaf segments (apex, incision, base) were more pronounced at low RH levels. Independent of the given RH level, the absolute contractions within the incision region ofD. cooperiwere significantly higher than in all other segments of this species and ofD. ecklonis. The more pronounced contraction ofD. cooperileaves was linked mainly to the elastic properties of the central vascular strand, which is approximately twice as flexible as that ofD. ecklonisleaves.