Hydrangea crassa (Hand.-Mazz.) Y.De Smet & C.Granados — Leatherleaf hydrangea vine

Introduction

The leatherleaf hydrangea vine, Hydrangea crassa, is a distinctive high-elevation member of Section Schizophragma confined, on present evidence, to northwestern Yunnan. It is a deciduous woody climber of montane forests at approximately 2300–2900 m, bearing thickly papery leaves with a pale or glaucous lower surface densely covered by gray or yellow-brown hairs. Young branchlets and petioles are also conspicuously hairy, giving the plant a substantially more robust and heavily indumented appearance than many of its relatives (Wei & Bartholomew 2001; Royal Botanic Gardens, Kew 2026).

Its most remarkable feature is floral rather than vegetative. Hydrangea crassa lacks the showy sterile marginal flowers that otherwise characterize almost the entire former genus Schizophragma. Its inflorescences consist entirely of fertile flowers. This is sufficiently unusual that older identification keys separate S. crassum from every other Chinese Schizophragma at the first couplet. Yet modern phylogenetic work retains the species within Section Schizophragma, illustrating an important broader theme in Hydrangea: striking individual morphological characters can be gained, lost, or modified without necessarily marking deep lineage boundaries (Wei & Bartholomew 2001; Yang et al. 2024).

The species was described by Handel-Mazzetti in 1922 as Schizophragma crassum and transferred to broad Hydrangea by De Smet and Granados in 2015. Current major backbones accept the species and restrict its native range to northwestern Yunnan. They place three additional names beneath it: Schizophragma crassum var. ellipticum J.Anthony, S. hsitaoanum Chun, and S. crassum var. hsitaoanum (Chun) C.F.Wei (Royal Botanic Gardens, Kew 2026; WFO 2026).

Tree TSAR does not interpret all three of those names as uninformative synonyms. Liu & Zhu (2009) examined extensive type and authoritative material and concluded that var. ellipticum was the correct name for the entity that had also been called S. hsitaoanum and var. hsitaoanum. Their treatment was supported by leaf-epidermal characters. Together with the geographic and morphological distinctions recorded in Flora of China, that evidence supports recognition of a repeatable infraspecific entity. Tree TSAR therefore accepts Hydrangea crassa var. elliptica as a botanical variety rather than reducing the names without qualification. Population-level nuclear data remain desirable to test the strength and continuity of that differentiation.

The parent Hydrangea crassa page consequently represents the species as a whole, while H. crassa var. elliptica is an accepted infraspecific taxon within it rather than a second species. Variety rank communicates a geographically and morphologically structured component of H. crassa without implying that complete evolutionary independence has been demonstrated.

Horticultural and Agricultural Uses

No securely established horticultural tradition for authentic Hydrangea crassa was located. This contrasts sharply with H. ampla, H. hydrangeoides, and increasingly H. fauriei. Its high-elevation Yunnanese origin, thick leaves, dense indument, and unusual lack of sterile flowers would nevertheless make it a botanically distinctive collection plant if well-documented material were introduced.

Because sterile marginal flowers provide much of the visual appeal associated with the familiar schizophragmas, H. crassa would probably appeal more strongly to botanical and conservation collections than to the mass ornamental trade. Its greatest horticultural value may therefore lie in representing the morphological breadth of Hydrangea and providing living material for comparative study. Any future introduction should be linked to a voucher and precise locality, particularly because the relationship between typical plants and H. crassa var. elliptica remains incompletely understood.

Conservation Concerns

No formal global IUCN assessment was located for Hydrangea crassa. Its known range is considerably narrower than that of most mainland species in the section, with current Kew treatment restricting it to northwestern Yunnan and Flora of China placing it in montane forests at 2300–2900 m.

That combination of restricted geography and high-elevation habitat makes contemporary population information especially desirable, but it does not by itself establish that the species is threatened. Tree TSAR should avoid converting apparent rarity in literature or horticulture into a conservation category. Field confirmation of historical localities, estimates of population size and continuity, and representation of both typical H. crassa and H. crassa var. elliptica in ex situ collections would provide a much stronger basis for future assessment.

Additional Information

Flora of China — Schizophragma crassum (opens in a new tab): morphology, montane habitat, and the distinctive absence of sterile flowers.

Liu & Zhu (2009) (opens in a new tab): type and epidermal evidence concerning var. ellipticum and the hsitaoanum names.

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)

Liu W, Zhu X-Y (2009) The identity of some taxa of Schizophragma (Saxifragaceae). Journal of Systematics and Evolution 47(2): 151–161. https://doi.org/10.1111/j.1759-6831.2009.00014.x (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 crassa (Hand.-Mazz.) Y.De Smet & C.Granados. Plants of the World Online. https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:77152138-1 (opens in a new tab)

Wei Z, Bartholomew B (2001) Schizophragma Siebold & Zuccarini. In: Wu ZY, Raven PH (eds.) Flora of China, vol. 8. Science Press, Beijing & Missouri Botanical Garden Press, St. Louis, pp. 408–410. https://www.iplant.cn/foc/pdf/Saxifragaceae.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)