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J R Soc Interface. 2014 Oct 6;11(99). pii: 20140611. doi: 10.1098/rsif.2014.0611.

Bouldering: an alternative strategy to long-vertical climbing in root-climbing hortensias.

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Department of Biology, Research Group Spermatophytes, Ghent University, K.L. Ledeganckstraat 35, Ghent 9000, Belgium Departamento de Botánica, Instituto de Biología, Universidad Nacional Autónoma de México, Apartado Postal 70-367, Coyoacán 04510, Distrito Federal, Mexico
Laboratoire de Botanique et d'Écologie Végétale Appliquées, IRD, UMR AMAP, BPA5, Nouméa 98800, New Caledonia.
Department of Botany, University of Cape Town, Rondebosch 7701, Cape Town, South Africa Climate Change Adaptation Division, South African National Biodiversity Institute, Kirstenbosch Research Centre, Private Bag x7, Claremont 7735, Cape Town, South Africa.
Faculty of Bioscience Engineering, Department of Forest and Water Management, Laboratory of Wood Technology, Ghent University, Coupure Links 653, Ghent 9000, Belgium.
Université Montpellier 2, UMR AMAP, Montpellier, F-34000 France; CNRS, UMR AMAP, Montpellier, F-34000 France.
Department of Biology, Research Group Spermatophytes, Ghent University, K.L. Ledeganckstraat 35, Ghent 9000, Belgium.
Department of Biology, Research Group Spermatophytes, Ghent University, K.L. Ledeganckstraat 35, Ghent 9000, Belgium Centro Regional del Bajío, Instituto de Ecología, A.C., Avenida Lázaro Cárdenas 253, Pátzcuaro 61600, Michoacán, Mexico.


In the Neotropics, the genus Hydrangea of the popular ornamental hortensia family is represented by climbing species that strongly cling to their support surface by means of adhesive roots closely positioned along specialized anchoring stems. These root-climbing hortensia species belong to the nearly exclusive American Hydrangea section Cornidia and generally are long lianescent climbers that mostly flower and fructify high in the host tree canopy. The Mexican species Hydrangea seemannii, however, encompasses not only long lianescent climbers of large vertical rock walls and coniferous trees, but also short 'shrub-like' climbers on small rounded boulders. To investigate growth form plasticity in root-climbing hortensia species, we tested the hypothesis that support variability (e.g. differences in size and shape) promotes plastic responses observable at the mechanical, structural and anatomical level. Stem bending properties, architectural axis categorization, tissue organization and wood density were compared between boulder and long-vertical tree-climbers of H. seemannii. For comparison, the mechanical patterns of a closely related, strictly long-vertical tree-climbing species were investigated. Hydrangea seemannii has fine-tuned morphological, mechanical and anatomical responses to support variability suggesting the presence of two alternative root-climbing strategies that are optimized for their particular environmental conditions. Our results suggest that variation of some stem anatomical traits provides a buffering effect that regulates the mechanical and hydraulic demands of two distinct plant architectures. The adaptive value of observed plastic responses and the importance of considering growth form plasticity in evolutionary and conservation studies are discussed.


biomechanics; phenotypic accommodation; phenotypic plasticity; plant architecture; stem anatomy; wood densitometry

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