Hydrangea obtusifolia (Hu) Y.De Smet & C.Granados — Chinese scrambling hydrangea

Introduction

The Chinese scrambling hydrangea, Hydrangea obtusifolia, is an evergreen woody climber or scrambling shrub of central China, generally reaching about 2–5 m. It grows in thickets on mountain slopes and among rock crevices, chiefly between about 600 and 1300 m, and is securely recorded from Gansu, Guizhou, Hubei, Shaanxi, and Sichuan. Its leathery leaves are relatively small—about 3.5–7 × 2–3.5 cm—usually obovate to elliptic, with cuneate bases and mostly entire, weakly serrate, or undulate margins (Wei & Bartholomew 2001).

Like H. barbara, it lacks enlarged sterile marginal flowers and produces terminal clusters composed entirely of small fertile flowers. The flowers bear 7–10 petals and 20–30 stamens, with an inferior 5–10-loculed ovary and a very short stout style. Its brown capsules are campanulate to turbinate, strongly ribbed, and contain winged seeds. These similarities explain why H. obtusifolia spent more than a century classified alongside the American Woodvamp hydrangea in Decumaria (Wei & Bartholomew 2001).

Its nomenclatural history is particularly instructive. Daniel Oliver first described the plant in 1888 as Decumaria sinensis from Augustine Henry's collection 3434 in the Yichang Gorge of Hubei, where Henry described it growing as a creeper hanging from a cliff. BSI Hu later described the same biological species as Schizophragma obtusifolium in 1934 and transferred it to Pileostegia the following year. Current Kew taxonomy recognizes all three names beneath Hydrangea obtusifolia (Royal Botanic Gardens, Kew 2026).

The apparently odd choice of the younger epithet obtusifolia rather than the older sinensis is nomenclaturally necessary. When De Smet et al. transferred the species to Hydrangea in 2015, they explicitly noted that Oliver's Decumaria sinensis could not supply the combination because of the pre-existing Hydrangea chinensis Maxim.; they therefore based the new combination on Hu's Schizophragma obtusifolium. Semantic Scholar (opens in a new tab)

Its sectional placement is less settled than its species identity. Raman et al. (2023) generated a new H. obtusifolia plastome and recovered it strongly with H. barbara, while also concluding that an older GenBank accession assigned to H. obtusifolia was probably misidentified. Yang et al. (2024), however, sampled a new vouchered Hubei H. obtusifolia and again recovered it immediately sister to Section Schizophragma, not to H. barbara. On that basis they established the monotypic Section Sinenses.

Tree TSAR retains Section Sinenses because it is part of our adopted Yang et al. infrageneric architecture, but this is a deliberately reviewable decision. Both conflicting studies rely primarily on plastid genomes. A multilocus nuclear or target-capture analysis using multiple vouchered populations of H. obtusifolia and H. barbara would be much more decisive than further comparisons of individual chloroplast accessions.

Horticultural and Agricultural Uses

Hydrangea obtusifolia is an uncommon but distinctive ornamental climber. Its evergreen, glossy foliage and clusters of small white fertile flowers give it a quieter appearance than climbing hydrangeas with large sterile sepals. Flower fragrance is consistently reported but described remarkably differently by different observers, from honey-like and pleasant to faint or even unpleasant, suggesting substantial subjectivity or perhaps variation among plants and flowering conditions (Sutton 2025).

The species performs best horticulturally in a warm, sheltered position with reasonably moist soil. It can grow in sun or shade, but flowering appears much poorer in deep shade than in H. barbara; summer warmth and good light on the mature climbing shoots seem particularly important. It remains uncommon in Western gardens and is still frequently encountered under its older name Decumaria sinensis (Sutton 2025).

Its cultivation history is unusually well documented. Oliver's original material came from Augustine Henry's 1887 Yichang collections, while Ernest Wilson certainly introduced material from the same general region to the Arnold Arboretum in the early twentieth century. Sutton notes that recent wild-origin introductions are difficult to trace, making old cultivated accessions potentially important but also raising questions about how much of the species' natural genetic variation is represented ex situ (Sutton 2025).

Conservation Concerns

The species has not received a global IUCN assessment in the sources reviewed here, but China's current national Red List of Higher Plants lists Decumaria sinensis—the same biological species—as Least Concern (LC) (Ministry of Ecology and Environment & Chinese Academy of Sciences 2023). This accords with a distribution across several central Chinese provinces rather than an extremely narrow endemic range.

Nevertheless, its comparatively sparse representation in modern Western collections should not be mistaken for wild rarity. Conversely, an LC national assessment does not resolve whether particular populations—especially the historical Yichang Gorge region or geographically peripheral populations—contain distinctive genetic structure. Given the unresolved relationship with H. barbara, geographically representative conservation sampling could have substantial evolutionary value.

Additional Information

Plants of the World Online — Hydrangea obtusifolia (opens in a new tab): — accepted nomenclature and complete three-name synonymy.

Trees and Shrubs Online — Hydrangea obtusifolia (opens in a new tab): — detailed systematic, horticultural, introduction-history, and cultivation discussion.

Flora of China — Decumaria sinensis (opens in a new tab): — morphology, habitat, phenology, and Chinese distribution.

References and Further Reading

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)

Huang SM, Bartholomew B (2001) Decumaria Linnaeus. In: Wu ZY, Raven PH (eds.) Flora of China, vol. 8. Science Press, Beijing & Missouri Botanical Garden Press, St. Louis, pp. 403. https://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=109459 (opens in a new tab)

Ministry of Ecology and Environment, Chinese Academy of Sciences (2023) 中国生物多样性红色名录—高等植物卷（2020）. https://www.mee.gov.cn/xxgk2018/xxgk/xxgk01/202305/W020230522536560832337.pdf (opens in a new tab)

Oliver D (1888) Decumaria sinensis Oliv. Hooker's Icones Plantarum 18: t. 1741. https://bsi.gov.in/uploads/userfiles/file/Rare%20Books/Hookers%20Icones%20Plantarum%20Vol.%208%28Third%20Series%29.pdf (opens in a new tab)

Raman G, Choi K-S, Lee EM, Morden CW, Shim H, Kang J-S, Yang T-J, Park S (2023) Extensive characterization of 28 complete chloroplast genomes of Hydrangea species: A perspective view of their organization and phylogenetic and evolutionary relationships. Computational and Structural Biotechnology Journal 21: 5073–5091. https://doi.org/10.1016/j.csbj.2023.10.010 (opens in a new tab)

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

Yang X, Xue T, Gao T, Liang Y, Smets EF, Gadagkar SR, Yu S (2024) An updated infrageneric classification based on phylogenomics and character evolution in Hydrangea (Hydrangeaceae). Taxon 73(2): 503–518. https://doi.org/10.1002/tax.13158 (opens in a new tab)