Hydrangea ampla (Chun) Y.De Smet & C.Granados — Windmill hydrangea vine

Introduction

The windmill hydrangea vine, Hydrangea ampla, is a large deciduous, aerial-rooting woody climber and the most geographically widespread mainland representative of Section Schizophragma. Mature plants can ascend high into trees or spread over cliffs and rock faces, producing broad terminal inflorescences surrounded by the conspicuous sterile flowers characteristic of the section. Each sterile flower normally consists primarily of a single enlarged, creamy-white sepal, giving flowering plants a distinctly different appearance from climbing hydrangeas whose sterile flowers bear several enlarged sepals. The leaves of typical H. ampla are relatively large, usually entire or only finely toothed toward the apex, and glabrous or only sparsely hairy beneath (Wei & Bartholomew 2001; Liu & Zhu 2011; Sutton 2025).

The species has one of the more confusing nomenclatural histories in Hydrangea. Daniel Oliver originally described the principal biological concept as Schizophragma integrifolium in 1890. When the former genus Schizophragma was incorporated into broad Hydrangea, however, the name Hydrangea integrifolia was already occupied by an unrelated Asian climbing species. De Smet and colleagues therefore used Chun's later name Schizophragma amplum as the basis for the combination Hydrangea ampla (De Smet et al. 2015). Current Plants of the World Online consequently lists S. amplum, S. integrifolium, and the historical denticulatum names beneath H. ampla (Royal Botanic Gardens, Kew 2026).

Tree TSAR interprets H. ampla somewhat more broadly than some current taxonomic backbones. Flora of China separated the central-Sichuan Schizophragma megalocarpum and the northeastern-Guangxi S. choufenianum as species, principally on fruit morphology and indument, whereas Liu & Zhu's later focused revision recognized neither as distinct within their broad S. integrifolium concept (Wei & Bartholomew 2001; Liu & Zhu 2011; Sutton 2025). Current Kew treatment has again accepted Hydrangea megalocarpa as a species, but no population-genomic or comparable integrative study has yet demonstrated that the large-fruited Sichuan plants constitute an independently evolving lineage.

Tree TSAR therefore includes both the Megalocarpa Form and Choufenianum Form within H. ampla. A Tree TSAR Form is not a formal botanical rank. These Forms receive their own narratives because each preserves a historically named and potentially meaningful regional expression of the species that would otherwise disappear into synonymy. Their separate treatment allows their morphology, geography, horticultural presence, and unresolved taxonomic questions to be documented without implying that current evidence supports species, subspecies, or varietal rank. Future genomic and population-level evidence could justify either renewed formal recognition or complete merger into ordinary H. ampla variation.

The limits of H. ampla remain imperfectly understood even beyond these Forms. Current Kew data report a broad range from the eastern Himalaya through southern China into Myanmar and Vietnam, while Liu & Zhu's revision concentrated on a more securely documented Chinese core. Sutton (2025) accordingly cautions that some peripheral records deserve renewed taxonomic scrutiny. The broad species concept should therefore be understood as a working evolutionary hypothesis rather than a claim that all geographic variation across this large range has already been tested genetically.

Within Section Schizophragma, typical H. ampla can usually be distinguished from H. hydrangeoides by its much less coarsely serrate leaves; from H. schizomollis by the absence of dense brown tomentum across the lower leaf surface; and from H. glaucescens by lacking the latter's strongly glaucous lower surface and conspicuous tufts of hair in the vein axils. These distinctions remain useful in the field even though the section as a whole has repeatedly demonstrated how easily individual vegetative characters can vary or converge (Liu & Zhu 2011; Sutton 2025).

Horticultural and Agricultural Uses

Hydrangea ampla has been cultivated in Europe for more than a century and remains better known to many gardeners under the name Schizophragma integrifolium. Early Western introductions included Ernest Wilson's Chinese collections, and later wild-origin accessions from Sichuan and other parts of China have added considerable variation to cultivated stocks. Plants can become substantial climbers, especially when allowed to ascend mature trees or large walls, and combine glossy foliage with broad summer inflorescences and unusually long, narrow sterile sepals (Sutton 2025).

The species tolerates woodland conditions, but established plants generally flower more freely when their upper growth reaches good light. This ecological transition from shaded rooting zones toward brighter canopy or cliff-edge growth is characteristic of many large forest climbers and helps explain why apparently vigorous plants in deep shade may remain relatively reluctant to flower. Cultivated material should also be interpreted cautiously: historical garden stocks, wild-origin accessions, and plants labelled H. megalocarpa or Schizophragma choufenianum may represent different points within the broader morphological range now treated here as H. ampla.

The Megalocarpa and Choufenianum Forms are especially useful horticulturally because collection names associated with those historical taxa continue to appear. Retaining those concepts as Tree TSAR Forms provides a way to discuss identifiable cultivated material without forcing the names into formal species rank.

Conservation Concerns

No formal global IUCN assessment has been located for Hydrangea ampla. Its broad working distribution and occurrence across numerous Chinese provinces suggest that the species as presently circumscribed is not narrowly endemic. Kew's Angiosperm Extinction Risk Predictions currently predicts the species to be not threatened, with confident model support, but this is a predictive screening result rather than a formal Red List assessment (Bachman et al. 2024; Royal Botanic Gardens, Kew 2026).

The broad species assessment should not be allowed to obscure potentially localized components of its diversity. The populations historically called S. megalocarpum and S. choufenianum may occupy much more restricted geographic areas than H. ampla as a whole. Even if they prove not to merit formal taxonomic rank, geographically distinctive populations can still contain evolutionary, ecological, or genetic diversity worthy of conservation. Improved population sampling across Sichuan, Guangxi, the southern Chinese range, and the reported peripheral populations in the Himalaya and Indochina would clarify both species limits and conservation priorities.

Additional Information

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

Trees and Shrubs Online — Hydrangea ampla (opens in a new tab): detailed horticultural, historical, and taxonomic discussion, including the megalocarpa and choufenianum problems.

Flora of China — Schizophragma (opens in a new tab): historical split treatment and diagnostic key to the Chinese species.

References and Further Reading

Bachman SP, Brown MJM, Leão TCC, Nic Lughadha EM, Walker BE (2024) Extinction risk predictions for the world's flowering plants to support their conservation. New Phytologist 242(2): 797–808. https://doi.org/10.1111/nph.19592 (opens in a new tab)

De Smet Y, Granados Mendoza C, Wanke S, Goetghebeur P, Samain M-S (2015) Molecular phylogenetics and new (infra)generic classification to alleviate polyphyly in tribe Hydrangeeae (Cornales: Hydrangeaceae). Taxon 64(4): 741–753. https://doi.org/10.12705/644.6 (opens in a new tab)

Liu W, Zhu X-Y (2011) Leaf epidermal characters and taxonomic revision of Schizophragma and Pileostegia (Hydrangeaceae). Botanical Journal of the Linnean Society 165(3): 285–314. https://doi.org/10.1111/j.1095-8339.2010.01101.x (opens in a new tab)

Royal Botanic Gardens, Kew (2026) Hydrangea ampla (Chun) Y.De Smet & C.Granados. Plants of the World Online. https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:77152136-1 (opens in a new tab)

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

Wei Z, Bartholomew B (2001) Schizophragma Siebold & Zuccarini. In: Wu ZY, Raven PH (eds.) Flora of China, vol. 8. Science Press, Beijing & Missouri Botanical Garden Press, St. Louis, pp. 408–410. https://www.iplant.cn/foc/pdf/Saxifragaceae.pdf (opens in a new tab)