Synonyms
- Cardiandra × agricola
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Introduction
The Crûg Farm herb hydrangea, Hydrangea × agricola, is a deliberately created garden hybrid between the Japanese H. alternifolia and Taiwanese herb hydrangea, H. densifolia. Both parents belong to section Cardiandra, the subshrub branch of subgenus Cardiandra. Although their leafy shoots can give these plants an herbaceous appearance, they persist through a woody or suffrutescent basal and rhizomatous framework rather than disappearing completely into an underground rhizome as the species of section Deinanthe do (Yang et al. 2024).
Julian Shaw described the hybrid in 2008 as Cardiandra × agricola, from a cross made at Crûg Farm Plants in North Wales between C. alternifolia and C. formosana. The latter name is now treated as a synonym of Hydrangea densifolia. The original description characterized the offspring as intermediate between their parents, particularly in the sterile marginal flowers, and designated a cultivated seedling from Crûg Farm as the type (Shaw 2008). Crûg Farm Nursery (opens in a new tab)
The hybrid is especially useful for understanding section Cardiandra because its parents represent geographically separated Japanese and Taiwan–Zhejiang lineages. Their ability to produce viable cultivated offspring demonstrates that their evolutionary differentiation has not resulted in complete reproductive incompatibility. That fact does not collapse the two parental species, but it does illustrate the comparatively porous reproductive boundaries that can persist among related plant lineages.
Horticultural and Agricultural Uses
Hydrangea × agricola exists because of horticulture. The original cross was undertaken to combine characteristics of the Japanese and Taiwanese parents, and its seedlings proved variable enough for selections to be made from the progeny. ‘Crûg’s Pink’ is among the cultivated forms associated with the hybrid. Crûg Farm Nursery (opens in a new tab)
Shaw (2008) recommended the moist, humus-rich, semi-shaded conditions suited to cultivated Cardiandra generally. Division of the perennial basal system is particularly appropriate for named selections because it produces genetically identical plants. Seedlings produced sexually would instead reshuffle the parental genomes and should not automatically be regarded as equivalent to an established cultivar.
Conservation Concerns
As a horticulturally created hybrid, H. × agricola is not itself a wild conservation unit requiring a conventional species-level threat assessment. Its conservation value lies chiefly in documented living material, especially plants whose parentage and provenance remain traceable.
Cultivation of the hybrid should not be confused with ex situ conservation of its parental species. A garden clone containing genes from both parents cannot replace genetically representative populations of either H. alternifolia or H. densifolia.
Additional Information
References and Further Reading
Shaw JMH (2008) Three new Crûg Farm introductions. The Plantsman, New Series 7(1): 39–43. https://www.crug-farm.co.uk/content/uploads/press%20releases/2008/Crug%20Farm%20Intros.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)