The complex leaves of the monkey's comb (Amphilophium crucigerum, Bignoniaceae): a climbing strategy without glue

Monkey's comb (Amphilophium crucigerum) is a widely spread neotropical leaf climber that develops attachment pads for anchorage. A single complex leaf of the species comprises a basal pair of foliate, assimilating leaflets and apical, attaching leaflet tendrils. This study aims to analyze these leaves and their ontogenetic development for a better understanding of the attachment process, the form-structure-function relationships involved, and the overall maturation of the leaves.

Thorough morphometrical, morphological, and anatomical analyses incorporated high-resolution microscopy, various staining techniques, SEM, and photographic recordings over the entire ontogenetic course of leaf development.

The foliate, assimilating leaflets and the anchorage of the more apical leaflet tendrils acted independently of each other. Attachment was achieved by coiling of the leaflet tendrils and/or development of attachment pads at the tendril apices that grow opportunistically into gaps and fissures of the substrate. In contact zones with the substrate, the cells of the pads differentiate into a vessel element-like tissue. During the entire attachment process of the plant, no glue was excreted.

The complex leaves of monkey's comb are highly differentiated organs with specialized leaf parts whose functions-photosynthesis or attachment-work independently of each other. The function of attachment includes coiling and maturation process of the leaflet tendrils and the formation of attachment pads, resulting in a biomechanically sound and persistent anchorage of the plant without the need of glue excretion. This kind of glue-less attachment is not only of interest in the framework of analyzing the functional variety of attachment structures evolved in climbing plants, but also for the development of innovative biomimetic attachment structures for manifold technical applications.