Hydrangea integrifolia Hayata — Philippine sprawling hydrangea

Introduction

Philippine sprawling hydrangea is a vigorous evergreen, woody root-climber native to Taiwan and the Philippines, where it ascends trees and rocky slopes in humid mountain forests. Taiwanese plants occur in dense forest at roughly 1,000–2,800 m elevation and can develop into substantial canopy climbers. The leathery, usually essentially untoothed leaves, rounded to broadly umbel-like inflorescences, and generally small or scattered enlarged flowers give the species a relatively restrained appearance compared with the showier Mexican Hydrangea seemannii (Wei & Bartholomew 2001; Sutton 2025).

Its importance within Section Cornidia is much greater than its modest horticultural familiarity might suggest. Hydrangea integrifolia was the only Asian Cornidia sampled in the section-wide nuclear phylogeny of Granados Mendoza et al. (2021). It formed part of a strongly supported early-diverging lineage with the northwestern Mexican H. seemannii and the southern South American H. serratifolia: H. serratifolia was sister to a clade in which the sampled H. seemannii accessions were successive sisters of H. integrifolia. These three species therefore span almost the entire geographic extremes of the section despite being one another’s closest sampled relatives. Biogeographic reconstruction favored a New World origin for Cornidia itself and left long-distance dispersal from the Americas to Asia as an important explanation for the origin of the H. integrifolia lineage (Granados Mendoza et al. 2021).

The reproductive biology of H. integrifolia is equally distinctive. Functional dioecy, in which separate plants function primarily as male or female, was reconstructed as ancestral in Cornidia. Hydrangea integrifolia and H. seemannii instead possess genuinely hermaphroditic flowers, representing a reversal from that ancestral condition (Granados Mendoza et al. 2021). This shared reproductive shift reinforces their close relationship even though the two species now inhabit opposite sides of the Pacific.

The three temperate Cornidia can be surprisingly difficult to distinguish when their geographic provenance is unknown. Hydrangea integrifolia usually bears rounded, umbel-like inflorescences with enlarged flowers that are smaller and more irregularly scattered than those of H. seemannii. The latter generally has a flatter inflorescence surrounded by conspicuous enlarged marginal flowers. Hydrangea serratifolia more often produces a distinctly thyrse-like inflorescence, usually lacks enlarged flowers altogether, and remains functionally dioecious. Leaf toothing is less dependable than the name serratifolia might imply (Sutton 2025).

The present concept of H. integrifolia also incorporates a substantial early twentieth-century nomenclatural history. Hydrangea integra, H. glandulosa, H. cuneatifolia, and H. subintegra were described from Taiwanese or Philippine material but are now treated within H. integrifolia, together with the combination Cornidia integrifolia. This broad Taiwan–Philippines circumscription remains reasonable, but population-level sampling across both island systems would be valuable. In particular, the relationship between H. integrifolia and the little-studied Taiwanese H. taiwaniana remains one of the most important unresolved questions surrounding the Asian Cornidia.

Horticultural and Agricultural Uses

Among the tropical and subtropical climbing hydrangeas, H. integrifolia is unusually useful in temperate horticulture. Established plants are vigorous evergreen climbers capable of covering substantial walls or ascending mature trees, and cultivated experience in the Pacific Northwest and western Europe suggests greater cold tolerance than is typical of Cornidia. Trees and Shrubs Online gives it USDA Zones 7–9 and an RHS H4 rating, although provenance and local exposure undoubtedly influence performance (Sutton 2025).

Its flexibility is noteworthy. Plants have been grown as large wall climbers, allowed to ascend mature trees, trained as free-standing shrubs, and even clipped into tall hedges. Shade is tolerated, and flowering has been observed in very shady situations, although better illumination generally promotes heavier flowering. Because mature plants can produce extensive ground-level growth before finding additional supports, their eventual scale should be anticipated when they are planted near smaller trees or structures (Sutton 2025).

The species has also attracted interest as potential breeding material. Its combination of evergreen foliage, climbing architecture, relative cold tolerance, and considerable genetic distance from the familiar shrubby garden hydrangeas has made it a candidate for wide-crossing work in Hydrangea. Such breeding remains specialized, but H. integrifolia represents a particularly interesting reservoir of traits beyond those represented by the conventional macrophylla-type cultivar pool (Sutton 2025).

Conservation Concerns

Hydrangea integrifolia has not received a formal IUCN Red List assessment in the sources reviewed. Its occurrence in both Taiwan and the Philippines gives it a wider geographic footprint than many narrowly endemic Cornidia, but that broad distribution should not be confused with demonstrated population security. In Taiwan it is associated with humid mountain forest and rocky slopes, and much less is known about how Philippine populations compare genetically or demographically with Taiwanese ones (Sutton 2025).

The current taxonomic concept itself is therefore conservation-relevant. If the geographically separated Taiwanese and Philippine populations contain substantial internal structure, or if H. taiwaniana proves to represent a distinct closely related lineage, treating all Asian Cornidia as one homogeneous conservation unit would obscure that diversity. Population-level nuclear genomic sampling from both island systems would clarify not only species boundaries but also appropriate provenance units for ex situ collections.

Additional Information

Trees and Shrubs Online — Hydrangea integrifolia (opens in a new tab): detailed morphology, horticultural history, identification, and discussion of its relationship to the other temperate Cornidia.

Plants of the World Online — Hydrangea integrifolia (opens in a new tab): accepted nomenclature, distribution, and synonymy.

Flora of China — Hydrangea integrifolia (opens in a new tab): Taiwanese morphology, habitat, and distributional treatment.

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)

McClintock E (1957) A monograph of the genus Hydrangea. Proceedings of the California Academy of Sciences, Fourth Series 29(5): 147–256. https://www.biodiversitylibrary.org/part/51707 (opens in a new tab) https://doi.org/10.5281/zenodo.15905786 (opens in a new tab)

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

Wei Z, Bartholomew B (2001) Hydrangea. In: Wu ZY, Raven PH (eds.) Flora of China, vol. 8. Science Press, Beijing & Missouri Botanical Garden Press, St. Louis, pp. 411–422. https://www.iplant.cn/foc/pdf/Hydrangea.pdf (opens in a new tab)