Hydrangea oerstedii Briq. — Ruby sprawling hydrangea

Introduction

Ruby sprawling hydrangea is one of the giants of Section Cornidia: a robust, evergreen, functionally dioecious root-climber capable of ascending approximately 60 m into Costa Rican and Panamanian cloud-forest canopies. Mature stems can eventually curve downward again, sometimes bringing spectacular flowering growth back within a few metres of the forest floor. Unlike most members of the peruviana–oerstedii complex, it is genuinely common within suitable habitat and has been collected throughout the year (Samain et al. 2021).

Its foliage is large and variable in size but structurally consistent: flat, ovate to lanceolate-elliptic leaves with an acuminate apex and glandular-dentate margin. Young leaf undersides and flowering axes carry appressed white stellate hairs that are eventually shed, while free-growing mature branches become glabrous. Numerous acarodomatia occupy the junctions of the midrib and principal veins. The inflorescences can be enormous—up to roughly 28 cm across in the material measured by Samain et al.—and usually carry conspicuous enlarged marginal flowers. Their sepals mature through pinkish red and wine-red tones, while the small reproductive flowers carry pinkish-red to purple petals. “Ruby” is therefore not merely a decorative abstraction; red-purple pigmentation is genuinely characteristic of the flowering display (Samain et al. 2021).

The distinction between H. oerstedii and H. peruviana is one of the central taxonomic corrections of modern Cornidia research. The former is a Costa Rican–Panamanian species of cloud forest from roughly 1,100–2,500 m; the latter is a rare Ecuadorian species of somewhat lower-elevation rainforest and cloud forest. Hydrangea oerstedii has flat leaves with white abaxial pubescence and glandular teeth, whereas H. peruviana has slightly spoon-shaped foliage with reddish pubescence and serrate to weakly dentate margins. Treating one as a variety of the other obscures multiple independent morphological, geographical, ecological, and phylogenetic differences (Samain et al. 2021).

The nomenclature records the history of that confusion. The same lineage was originally named Cornidia radiata Oerst. and later Hydrangea oerstedii Briq.; it has also been treated as H. peruviana var. oerstedii (Briq.) Freire-Fierro. Tree TSAR accepts H. oerstedii at species rank and retains both of those names in its synonymy.

Molecularly, the picture within H. oerstedii is more complex than its clear distinction from true H. peruviana. Accessions identified as H. oerstedii appeared in more than one portion of the two-gene tree, and in Costa Rica some were repeatedly paired with nearby H. aff. albostellata. Granados Mendoza et al. interpreted this geography as suggestive of ongoing genetic exchange. The species therefore seems morphologically secure but genetically permeable where it encounters other Cornidia—another reminder that species boundaries and absolute reproductive isolation are not synonymous (Granados Mendoza et al. 2021).

Horticultural and Agricultural Uses

Of the tropical members of this complex, H. oerstedii is among the most promising horticulturally. Samain & Martínez Salas (2015) reported it in botanical cultivation and highlighted the ornamental potential of Neotropical Cornidia for their evergreen foliage, vigor, and unusual red or purple floral coloration. It is nevertheless far less widely grown than the hardier H. seemannii.

Its natural ecology provides useful clues. Hydrangea oerstedii can persist in disturbed cloud forest and near villages so long as a suitable host tree, very high humidity, and protection from intense direct sun remain. Mature plants may bend downward and flower close to ground level, a habit that could make an established specimen far more visually accessible than a climber flowering exclusively in the canopy (Samain et al. 2021).

At the same time, old horticultural accessions labelled H. peruviana or H. oerstedii deserve re-identification. Trees and Shrubs Online specifically cautions that cultivated plants carrying these names should be checked against the modern revision (Sutton 2025).

Conservation Concerns

The specialist revision assessed H. oerstedii as Near Threatened, not because it is presently rare, but because the Costa Rican and Panamanian cloud forests on which it depends continue to be reduced and fragmented. Its estimated area of occupancy was about 428 km². The authors regarded it as unusually robust for a Cornidia and observed it persisting after substantial disturbance where host trees remained (Samain et al. 2021).

That resilience should not be exaggerated. A root-climbing liana still requires structural support and humid forest conditions; wholesale removal of host trees would eliminate the very framework on which it survives. Functional dioecy also makes severe fragmentation potentially more consequential because reproductive individuals of opposite sex may become isolated from one another. The revision authors specifically identified dioecy as a possible additional vulnerability across Cornidia (Samain et al. 2021).

Plants of the World Online currently accepts H. peruviana var. oerstedii and gives it a much broader Costa Rica-to-Bolivia range. That treatment directly conflicts with the 2021 specialist evidence restricting H. oerstedii sensu stricto to Costa Rica and Panama and recognizing the South American plants as several other species (Royal Botanic Gardens, Kew 2026).

Additional Information

Open-access 2021 Hydrangea oerstedii revision (opens in a new tab): — exceptionally detailed field-based description of architecture, flower sex, morphology, habitat, and conservation.

Trees and Shrubs Online — peruviana/oerstedii complex (opens in a new tab): — horticultural perspective and modern identification summary.

iNaturalist observations for Hydrangea oerstedii (opens in a new tab): — useful for modern Costa Rican and Panamanian observations, but records filed under H. peruviana var. oerstedii may follow a broader taxonomy.

References and Further Reading

Granados Mendoza C, Martínez Salas EM, Goetghebeur P, Wanke S, Samain M-S (2021) Molecular phylogeny, character evolution, and biogeography of Hydrangea section Cornidia, Hydrangeaceae. Frontiers in Plant Science 12: 661522. https://doi.org/10.3389/fpls.2021.661522 (opens in a new tab)

Samain M-S, Granados Mendoza C, Martínez Salas EM (2021) 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. PhytoKeys 171: 91–153. https://doi.org/10.3897/phytokeys.171.56351 (opens in a new tab)

Samain MS, Martínez Salas EM (2015) Hydrangea hunting in the Neotropics. The Plantsman, New Series 14(1): 30–35. https://www.researchgate.net/publication/273124588_Hydrangea_hunting_in_the_Neotropics (opens in a new tab)

Sutton J (2025) Hydrangea species of Section Cornidia. Trees and Shrubs Online. International Dendrology Society. https://www.treesandshrubsonline.org/articles/hydrangea/hydrangea-species-of-section-cornidia/ (opens in a new tab)