Microspines in tropical climbing plants: a small-scale fix for life in an obstacle course

Abstract

Many climbing plants exhibit microspines on their stems, which facilitate attachment and prevent slipping and falling from host plant supports. Extending forwards via growth through complex environments and anchoring stems to substrates with minimal contact forces are key benefits to climbing plants. Microspines are also highly desirable features for new technologies and applications in soft robotics. Using a novel sled-like device, we investigated static and sliding attachment forces generated by stems in 10 species of tropical climber from French Guiana differing in size and climbing habit. Eight species showed higher static and sliding forces when their stems were pulled in the basal direction against a standard surface than in the apical direction. This anisotropic behaviour also suggests that tropical climbers have evolved different ratchet-like mechanisms which allows easy sliding forwards but is resistant to slipping downwards. The presence of a downwards “stick-slip” phenomenon, where static attachment is not significantly stronger than maximal sliding attachment, was present in most species apart from three representing relatively weak attachment by microspines. This indicates that diverse microspine attachment strategies exist in climbing plants. This diversity of functional properties in tropical climbers offers a range of potential design specifications for climbing strategies on different substrates for artificial climbing artefacts.

Failure without Tears: Two-Step Attachment in a Climbing Cactus

“…Spine and root deployment in the same plant reinforces recent ideas that climbing plants can combine different modes of attachment and optimise attachment under varied environmental conditions [24]. The cactus shows deployment strategies for both moving and still environments.…”

“…Comparisons of mechanical properties and morphology were tested via non-parametric Kruskal-Wallis tests, followed by Mann-Whitney post hoc tests carried out in the software PAST [34]. As in other studies of climbing plants, there was a difficulty of obtaining unequivocally separate individual plants from what are complex, highly branched, clonal life forms while sampling from the same habitats and geographical locations [24]. We therefore elected to apply non-parametric tests for comparing biomechanical values of median values and post hoc tests as well as non-parametric Spearman rank-order correlation coefficients.…”

Trellis-forming stems of a tropical liana Condylocarpon guianense (Apocynaceae): A plant-made safety net constructed by simple “start-stop” development

“…Above the point of attachment, the apical part of the climbing shoot had continued as a searcher in free space and then encountering a leafy shoot of the same trellis and the same species. At this point, it is hindered by an obstacle and unable to twine tightly ( Lehnebach et al., 2022 ) and roves loosely across some branches without actually twining ( Figure 12A , red arrow). This example illustrates that twining has initiated the TYPE II lianoid wood at a very early stage of development with only a radial diameter of 200 µm thickness of stiff wood ( Figure 12B ) and just below the actual phase of twining.…”

“…Sampled stems were selected at least 5 m apart, thus reducing but not eliminating the possibility that sampled shoots were derived from the same individual or same branch system of an individual. A similar sampling strategy was applied for sampling diverse twining lianas ( Lehnebach et al., 2022 ) and insured that the sampling regime remained in a similar environment and did not vary radically in terms of light and other factors.…”

A perspective on plant robotics: from bioinspiration to hybrid systems

“…Actuation and autonomous materials have already been mentioned in sections 5 and 6 and are crucial. Another of various examples for a multifunctional passive structure derived from plants are microscale attachment systems based on hooks and spines [32,[101][102][103][104] as stated in section 3. However, they are interesting not only as reversible interlocking and attachment solution in a technical scenario.…”