The climbing habit in palms: Biomechanics of the cirrus and flagellum.

Climbing palms in the Arecoideae (Desmoncus) and Calamoideae (rattan palms) both evolved cirrate leaves armed with hooks and grapnels for climbing. Some species of Calamoideae develop a different climbing organ known as the flagellum, which also bears hooks. The present study indicates that geometry and mechanical properties of the cirrus vary between species. Cirrate leaves are constructed to optimize bending and torsion in relation to the deployment of recurved hooks. Hook development, size, and strength vary along cirri and flagella and are consistent with observations of these attachment organs functioning as a ratchet mechanism: hooks increase in strength toward the base of attachment organs and always fail before the axis in strength tests. Hook size and strength differ between species and are related to body size and ecological preference. Larger species produce larger hooks, but smaller climbing palms of the understory deploy fine sharp hooks that are effective on small diameter supports as well as large branches and trunks. The ephemeral nature of climbing organs in palms provides a challenge to their life-history development, particularly in terms of mechanical constraints and remaining attached to the host vegetation; these differ significantly from many vines and lianas having more perennial modes of attachment.