The growth form of Croton pullei (Euphorbiaceae) - Functional morphology and biomechanics of a neotropical liana

Croton pullei (Euphorbiaceae) is a woody climber of the lowland rainforest in French Guyana and Surinam. During ontogeny, a shift from a juvenile free -standing growth phase to an older supported growth phase is observed. The following biomechanical parameters were studied: structural Young's modulus , structural torsional modulus, flexural stiffness and bend to twist ratios . Changes in anatomical development were also analysed for different stages of development of C. pullei which differ significantly in their mechanical properties. Free-standing plants show a nearly constant structural Young's modulus a nd structural torsional modulus during ontogeny, with flexural s tiffness increasing proportionally with the axial second moment of area. Th ese patterns are typical for "semi-self-supporting plants". in contrast, su pported plants show a significant decrease in structural Young's modulus in older stem parts, as well as a decrease in structural torsional modulus. D ue to the decrease in structural Young's modulus, flexural stiffness does n ot increase proportionally with the axial second moment of area. These patt erns are typical for non-self-supporting lianas. In all supported plants, a sudden transition occurs from early dense wood to a wood type with a much higher proportion of targe diameter vessels. In contrast, only the dense wo od type is present in all tested free-standing plants. The data are compare d with results from other climbing species of the same study area and discu ssed with reference to observed features characterizing the growth form and life history of C. pullei.