Hydrangea mollissima
Hainan bluebead hydrangea
Synonyms
- Dichroa mollissima
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Introduction
Hainan bluebead hydrangea, Hydrangea mollissima, is a woody shrub endemic to the island of Hainan, China. It grows in mixed forest in valleys at approximately 1000–1800 m and typically reaches about 2 m. Its insular distribution and strongly developed leaf indumentum make it one of the most readily characterized Chinese members of Section Dichroa (Wei & Bartholomew 2001).
The leaves are oblong-elliptic to obovate, about 8–16 cm long, with a cuneate base and teeth concentrated mainly above the middle. Their lower surfaces are densely villous, creating the soft texture reflected in the epithet mollissima. The upper surfaces are much less hairy to essentially glabrous at maturity. Inflorescences are corymbose cymes approximately 5–7 cm long and around 10 cm wide. Flowers bear five short ovate calyx lobes and white or blue petals, with ten to twelve stamens (Wei & Bartholomew 2001).
The fruit also helps distinguish the species. Rather than the nearly spherical berry common in several relatives, H. mollissima produces an oblong berry, approximately 4.5 × 6 mm, which may be pubescent or glabrous. The ovary is semi-inferior, and the flowers usually have three or four robust styles. Flowering occurs in June and July, followed by fruit from September into December (Wei & Bartholomew 2001).
Unlike several of the newer bluebead species, its placement within Section Dichroa has direct molecular support. Dichroa mollissima was transferred into broad Hydrangea by De Smet et al. (2015), producing the current combination Hydrangea mollissima (Merr.) Y.De Smet & C.Granados. Yang et al. (2024) subsequently included a Hainan accession in their plastome dataset; H. mollissima was one of the five traditionally recognized Section-Dichroa species directly sampled in their expanded phylogenomic analysis. doczz.net (opens in a new tab)
Its sectional placement is consequently among the more secure in this batch. The remaining scientific questions lie principally within the species: how strongly are Hainan populations differentiated from one another, how much genetic variation survives among the island's montane forest fragments, and does the species show any historical introgression with the widespread H. febrifuga complex?
The species is nomenclaturally simple. Merrill described it as Dichroa mollissima from Hainan material, and that basionym remains its only currently recognized synonym (Royal Botanic Gardens, Kew 2026).
Horticultural and Agricultural Uses
Hainan bluebead hydrangea has little documented horticultural presence outside botanical collections. Its densely soft lower leaf surfaces, blue or white flowers, and bluebead-type fruit make it visually distinctive, but its subtropical montane origin suggests limited cold tolerance.
The combination of an island provenance and a comparatively high-elevation subtropical habitat could make authentic material useful for comparative horticultural studies. It may differ in climatic response from both lowland tropical H. febrifuga populations and continental montane relatives.
No established agricultural or medicinal use specific to H. mollissima was located. Traditional medicinal claims associated with “changshan” should not automatically be transferred from H. febrifuga to this species merely because both were formerly classified in Dichroa.
Conservation Concerns
Hainan bluebead hydrangea is a genuine island endemic, and China’s comprehensive vascular-plant Red List assessed Dichroa mollissima as Near Threatened (NT) (Ministry of Environmental Protection & Chinese Academy of Sciences 2013). That category is consistent with a species confined to Hainan's montane and valley forests but not documented as undergoing the severe decline required for a threatened category.
The assessment nevertheless predates much of the recent reorganization of Hydrangea and should eventually be revisited with modern population data. Hainan has experienced extensive historical forest alteration, and a montane understory shrub can remain locally present while losing connectivity among populations.
Conservation should therefore represent the species across multiple mountains or watersheds rather than assuming one protected population captures the evolutionary diversity of the island endemic. Population genomics would be particularly useful for detecting fragmentation and identifying genetically distinctive local populations.
Additional Information
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) Dichroa. In: Wu ZY, Raven PH (eds.) Flora of China, vol. 8. Science Press, Beijing & Missouri Botanical Garden Press, St. Louis, pp. 404–406. https://www.iplant.cn/foc/pdf/Dichroa.pdf (opens in a new tab)
Merrill ED (1923) Diagnoses of Hainan plants, II. The Philippine Journal of Science 23(3): 237–268. https://www.biodiversitylibrary.org/item/88959#page/266 (opens in a new tab)
Ministry of Environmental Protection, Chinese Academy of Sciences (2013) 中国生物多样性红色名录—高等植物卷. https://www.mee.gov.cn/gkml/hbb/bgg/201309/W020130917614244055331.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)