Abstract: The climbing growth form has appeared several times during palm evolution and in phylogenetically distant groups. Among the 2700 species recognised in the Arecaceae, more than 500 are climbers. This study deals with species belonging to the two subfamilies, which include climbing forms, the Arecoideae and the Calamoideae, from South America and South-east Asia respectively. The main objective is to understand the mechanical, morphological and developmental traits linked to the climbing habit in a family that lacks secondary growth. The results are discussed using recent phylogenetic reconstructions and are compared with previous studies on the mechanical architecture of dicotyledonous lianas. The first part deals with the mechanical architecture and development of axes. The results emphasize the mechanical role of the leaf sheath and specific adaptations of the stem for the climbing habit in each subfamily. In the second part, morphological and structural organisation of attachment organs (flagellum and cirrus) are investigated. Breaking forces of hooks and acanthophylls, and the variations of mechanical properties along cirri and flagellae are discussed in terms of the plant ecology, its potential for occupying space and its attachment to supports. The results suggest that the apparently strongly convergent evolution towards the climbing habit has in fact produced specific mechanical architectures according to the phylogenetic constraints of different genera. In both subfamilies the occurrence of the climbing growth form may have resulted from heterochronic processes, involving the reduction of the establishment phase that characterise arborescent palms.
Calamus acanthospathus (Calamoideae- Arecaceae) in Yunnan, China
