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

Abstract

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.

Molecular phylogenetics and new (infra)generic classification to alleviate polyphyly in tribe Hydrangeeae (Cornales: Hydrangeaceae)

“…& Thomson, Platycrater Siebold & Zucc., Schizophragma Siebold & Zucc. ), encompassing warm temperate to tropical species (Table 1) with shrubby, herbaceous or root-climbing growth forms (Samain & al., 2010;Granados Mendoza & al., 2014;Fig. 1).…”

Repeatome landscapes and cytogenetics of hortensias provide a framework to traceHydrangeaevolution and domestication

“…Molecular phylogenetic studies have shown the monophyly of Hydrangea s.l. with two main clades called Hydrangea clade I and II (Samain et al, 2010;Mendoza et al, 2013Mendoza et al, , 2014De Smet et al, 2015;Raman et al, 2023). Several Hydrangea species native to Asia, including H. macrophylla and H. serrata, were brought to Europe about 200 years ago and since have been improved to serve as ornamental plants (Iwatsuki et al, 2001;Rinehart et al, 2006;Uemachi et al, 2014).…”

On Hydrangea peruviana, an endangered species from Ecuador, and Hydrangea oerstedii, very common in Costa Rica and Panama, and seven threatened Central and South American Hydrangeas, which have been confounded with these

“…The representatives of this section occur from northern Mexico to southern Chile and Argentina with one species, Hydrangea integrifolia Hayata, in southeastern Asia ( Samain et al 2014 ; Samain and Martínez Salas 2015 ; Samain et al 2019 ). All taxa are evergreen root climbers growing up to 60 m high in the canopy of mostly primary forests, or rarely on boulders and rock walls ( Granados Mendoza et al 2014 ), generally functionally dioecious, rarely monoecious, with coriaceous leaves and hortensia-like whitish-, greenish-, yellowish-, reddish- or purplish-tinged inflorescences, with or without enlarged marginal flowers.…”