Hydrangea zhewanensis P.S.Hsu & X.P.Zhang — Zhejiang hydrangea

Introduction

Zhejiang hydrangea, Hydrangea zhewanensis P.S.Hsu & X.P.Zhang, is a small woody shrub of southeastern Anhui and northern Zhejiang, China. Tree TSAR accepts it in Subgenus Dichroa and provisionally places it in Section Stylosae. This is a best-fit placement rather than a direct phylogenomic result: De Smet et al. (2015) listed H. zhewanensis as “Stylosae ?” in their broad-Hydrangea synthesis, and Flora of China keys the species immediately against H. stylosa while also noting affinity to H. macrophylla. Yang et al. (2024) did not directly sample H. zhewanensis, so the sectional assignment remains provisional pending authenticated phylogenomic sampling (De Smet et al. 2015; Wei & Bartholomew 2001; Yang et al. 2024).

The species is morphologically distinctive enough to retain independently. It forms shrubs about 0.7–1.5 m tall, with elliptic to rhomboid-elliptic serrate leaves and corymbose cymes bearing three or four enlarged bluish marginal sepals. Its short, thick styles, yellow anthers, and oblong-ovoid capsule distinguish it sharply from typical H. stylosa, which has longer slender styles, blue anthers, and a more nearly subglobose capsule. Those differences are important reasons to treat the Stylosae assignment as provisional rather than collapsing H. zhewanensis into H. stylosa. The historical application of H. macrophylla var. normalis to this plant is treated by Tree TSAR as a misapplication rather than a nomenclatural synonym (Wei & Bartholomew 2001).

Its native records come from stream banks, valley thickets, and mountain slopes at roughly 600–1,500 m. The combination of eastern Chinese geography, its historical association with the Stylosae complex, and the provisional sectional assignment makes H. zhewanensis especially valuable for future nuclear sampling. Authenticated material should test whether it is genuinely embedded within Section Stylosae or represents a nearby lineage that warrants reassessment of sectional boundaries.

Horticultural and Agricultural Uses

No substantial, reliably documented horticultural or agricultural tradition was located for H. zhewanensis. Its compact stature, bluish enlarged flowers, and eastern Chinese woodland ecology could make it useful to specialist Hydrangea collections, but living material is most valuable when provenance is retained so that cultivated plants can contribute to the unresolved sectional question. Generic cultivation advice should not be substituted for observations from authenticated accessions.

Conservation Concerns

No formal IUCN Red List assessment was located. Kew records a relatively restricted native range in southeastern Anhui and northern Zhejiang and its current angiosperm extinction-risk model predicts the species to be threatened with confident model support; that result is a screening prediction, not a formal Red List category (Royal Botanic Gardens, Kew 2026; Bachman et al. 2024).

Field verification of populations across the two-province range would serve both conservation and systematics. Voucher-backed occurrence data, population size and habitat-condition measurements, and nuclear sampling could establish whether the known range is genuinely narrow while directly testing the provisional placement of the species in Section Stylosae.

Additional Information

Plants of the World Online — Hydrangea zhewanensis (opens in a new tab): accepted name, distribution, publication data, and extinction-risk prediction.

Flora of China — Hydrangea zhewanensis (opens in a new tab): morphological description, habitat, elevation, and regional distribution.

World Flora Online — Hydrangea zhewanensis (opens in a new tab): nomenclatural cross-reference and Flora of China-derived description.

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)

Royal Botanic Gardens, Kew (2026) Hydrangea zhewanensis P.S.Hsu & X.P.Zhang. Plants of the World Online. https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:932912-1 (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)

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)