Hydrangea tomentella (Hand.-Mazz.) Y.De Smet & C.Granados — Rusty evergreen climbing hydrangea

Introduction

The rusty evergreen climbing hydrangea, Hydrangea tomentella, is the more geographically restricted of the two species in Section Pileostegia, an old segregate-genus lineage now placed within Subgenus Decumaria. It is an evergreen climbing or prostrate woody shrub of valley forests in southeastern China, documented from Fujian, Guangdong, Guangxi, Hunan, and Jiangxi. Its closest relative is the much more widespread H. viburnoides: the two form a strongly supported pair in the plastid phylogeny of Yang et al. (2024), while an earlier morphological and leaf-epidermal revision independently retained them as the two species of Pileostegia (Liu & Zhu 2011).

The two are readily distinguishable in the field. Branchlets, leaves, and inflorescences of H. tomentella are densely clothed in rusty-brown stellate hairs, producing the conspicuous indument that motivates its Tree TSAR common name. Its leaves tend to be oblong to obovate-oblong with rounded or shallowly cordate bases. H. viburnoides, by contrast, is essentially glabrous and normally has narrower elliptic to oblanceolate leaves with cuneate or truncate bases. H. tomentella therefore represents much more than a hairy local variant of its sister species: morphology and geography together define a consistently recognizable entity, and no current evidence warrants reducing its rank. Trees and Shrubs Online (Liu & Zhu 2011; Yang et al. 2024)

The species was originally described as Pileostegia tomentella Hand.-Mazz. and was later transferred to Schizophragma before the phylogenetic restructuring of Hydrangeeae brought it into broad Hydrangea in 2015. Its small synonym burden reflects the comparative stability of its biological concept once recognized. Plants of the World Online (De Smet et al. 2015; Yang et al. 2024)

Horticultural and Agricultural Uses

Hydrangea tomentella remains more horticultural possibility than established garden plant. Unlike H. viburnoides, it has not been identified with confidence in established Western collections. Sutton (2025) reports that two attempts to introduce authentic Chinese material failed, while a Vietnamese collection circulated as FMWJ 13444 has sometimes been associated with H. tomentella but does not fit either recognized species particularly well: its young stems bear shaggy whitish hairs, while its leaves are nearly glabrous and have cuneate rather than rounded bases. That collection should therefore not be used to broaden the circumscription or range of H. tomentella without renewed study. Trees and Shrubs Online (Sutton 2025)

If securely introduced, the species would be horticulturally distinctive for precisely the characters that diagnose it in nature: evergreen climbing architecture combined with its rusty stellate indument. For now, however, the absence of authenticated, established cultivated material is itself part of the species' story and is more informative than speculative cultivation advice.

Conservation Concerns

No formal IUCN Red List assessment was located. The species occupies a substantially smaller known range than H. viburnoides and has been reported from valley forests at roughly 300–700 m. Kew's Angiosperm Extinction Risk Predictions dataset currently predicts H. tomentella to be threatened with high model confidence, but this is a predictive screening result rather than a formal conservation assessment and should be represented as such. Trees and Shrubs Online (Bachman et al. 2024; Royal Botanic Gardens, Kew 2026)

The combination of a comparatively restricted distribution, limited ecological information, and little or no securely documented ex situ representation makes better field documentation valuable. A defensible formal assessment would require contemporary population records, habitat-condition data, and reliable estimates of range and occupancy rather than inference from the species' apparent rarity alone.

Additional Information

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 tomentella (Hand.-Mazz.) Y.De Smet & C.Granados. Plants of the World Online. https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:77152134-1 (opens in a new tab)

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