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Hydrangea macrocarpa Hand.-Mazz.

Silverback hydrangea

Synonyms
  • Hydrangea heteromalla var. mollis Rehder
  • Hydrangea mollis (Rehder) W.T.Wang
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Introduction

Silverback hydrangea (Hydrangea macrocarpa Hand.-Mazz.) is a large shrub or small tree of the mountains of southern Sichuan and northern Yunnan. It belongs to the difficult H. heteromalla complex and closely resembles woolly hydrangea in its broad corymbose inflorescences and densely hairy leaves. The distinction lies in the details: H. macrocarpa has a densely gray-white, long-tomentose lower leaf surface and characteristically larger capsules, usually about 3–4 mm across, with a strongly projecting conical apex. The name itself refers to these comparatively large fruits.

The species has sometimes been reduced to H. heteromalla, notably through the name H. heteromalla var. mollis. Tree TSAR provisionally retains species rank because the combination of dense long tomentum, fruit dimensions, geography, and current specialist recognition provides a plausible diagnosable unit. The evidentiary weakness is molecular: H. macrocarpa was not sampled in the plastome analysis of Yang et al. (2024). Its independence therefore remains less strongly tested than that of H. bretschneideri, H. sungpanensis, or H. xanthoneura.

This is consequently a species for which nomenclature is ahead of phylogenomics. Properly identified nuclear samples from southern Sichuan and northern Yunnan could either strengthen the present treatment or demonstrate that macrocarpa represents a regional expression of another member of the complex.

Horticultural and Agricultural Uses

Hydrangea macrocarpa is poorly represented in documented horticulture under its own name. Plants of the wider complex have often moved through collections as H. heteromalla, and confident identification requires mature foliage and fruit as well as flowers.

The densely silver-white lower leaf surface should give authentic material considerable ornamental interest. Because its distinction depends partly on characters that are easily lost when specimens are incompletely documented, botanical gardens cultivating wild-origin material can contribute directly to taxonomic understanding by preserving provenance and recording fruit characters.

Conservation Concerns

The documented native range is relatively restricted compared with those of H. heteromalla and H. paniculata, centering on southern Sichuan and northern Yunnan at roughly 2500–3500 m. It occurs in mixed forest, thickets, valleys, and streamside mountain habitats.

The absence of a well-developed modern population-genetic treatment makes it difficult to separate conservation rarity from taxonomic uncertainty. If H. macrocarpa proves to be a genuinely discrete lineage, its comparatively limited range would make accurate mapping and representation in ex situ collections more significant than a broad heteromalla treatment implies.

Additional Information

References and Further Reading

Handel-Mazzetti H (1925) Plantae novae Sinenses, diagnosibus brevibus descriptae a Dre. Heinr. Handel-Mazzetti (35. Fortsetzung). Anzeiger der Akademie der Wissenschaften in Wien, Mathematisch-Naturwissenschaftliche Klasse 62: 143–150. https://www.oeaw.ac.at/fileadmin/service/basis/archiv/pdf/digilit/DOKUMENTATION-02.pdf

Sutton J (2025) Hydrangea heteromalla. Trees and Shrubs Online. International Dendrology Society. https://www.treesandshrubsonline.org/articles/hydrangea/hydrangea-heteromalla/

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

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