Hydrangea densifolia
Taiwanese herb hydrangea
Synonyms
- Cardiandra densifolia
- Cardiandra alternifolia var. binata
- Cardiandra formosana
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Introduction
The Taiwanese herb hydrangea, Hydrangea densifolia, is a perennial subshrub native to Taiwan and Zhejiang in southeastern China. Its leaves are characteristically concentrated toward the distal portion of the stem, often in a group of four to eight, providing one of the clearest vegetative distinctions from the more evenly alternate leaves of H. alternifolia. Current global taxonomy includes Cardiandra densifolia, C. formosana, and C. alternifolia var. binata within H. densifolia (Royal Botanic Gardens, Kew 2026).
The phylogenetic position of H. densifolia deserves more cautious wording than that of several other Cardiandra species. Tagane et al.'s (2022) MIG-seq analysis that resolved H. marunoi, H. amamiohsimensis, H. moellendorffii, and H. alternifolia did not include H. densifolia. Consequently, the Taiwanese herb hydrangea should not yet be inserted into the southern three-species nuclear topology by inference alone.
Earlier chloroplast work nevertheless provides an important geographic clue. Setoguchi et al. (2006) recovered Taiwanese and Ryukyu Cardiandra populations together in a plastid lineage distinct from sampled Chinese and mainland-Japanese populations and interpreted much of the pattern in the context of Quaternary land connections. Because chloroplasts record only the organellar history of the plants, that result is best regarded as evidence of biogeographic history rather than a final statement of the organismal species tree. PubMed (opens in a new tab)
This remaining uncertainty makes H. densifolia particularly interesting: it is morphologically distinctive and taxonomically well established, yet its exact relationship to the better-resolved southern Cardiandra species would benefit from modern nuclear sampling spanning both Taiwan and Zhejiang.
Horticultural and Agricultural Uses
Hydrangea densifolia has a meaningful place in specialist horticulture and was historically circulated under the name Cardiandra formosana. That older name is particularly relevant because it was the Taiwanese parent named in Shaw's original description of Cardiandra × agricola. Under current taxonomy, that cross is H. alternifolia × H. densifolia (Shaw 2008). Crûg Farm Nursery (opens in a new tab)
Its compact subshrub habit lends itself to shaded woodland gardens, where moist, humus-rich soil accommodates the same basic ecological architecture as related Cardiandra. For scientific collections, provenance from Taiwan versus Zhejiang should be retained. The disjunction is potentially informative, and future nuclear work may reveal structure that anonymous garden material can no longer reconstruct.
Conservation Concerns
The 2017 Red List of Vascular Plants of Taiwan assessed the Taiwanese component of H. densifolia as Least Concern (LC). That is a regional assessment and should not be interpreted automatically as a global evaluation encompassing the Zhejiang populations. 臺灣生命大百科 (opens in a new tab)
Kew also reports a model-based Angiosperm Extinction Risk Prediction of “threatened” for the species. This is a predictive screening result rather than a formal Red List assessment, so the two pieces of information are not directly contradictory: one evaluates documented Taiwanese status, while the other estimates potential global risk from available plant data (Royal Botanic Gardens, Kew 2026).
The outstanding conservation need is therefore better range-wide information, particularly from continental populations and from genetically representative material on both sides of the Taiwan Strait.
Additional Information
References and Further Reading
Editorial Committee of the Red List of Taiwan Plants (2017) The Red List of Vascular Plants of Taiwan, 2017. Endemic Species Research Institute, Forestry Bureau, Council of Agriculture, Executive Yuan and Taiwan Society of Plant Systematics, Nantou. https://www.tbri.gov.tw/Uploads/userfile/A15_7/2018-12-19_1139102115.pdf (opens in a new tab)
Setoguchi H, Yukawa T, Tokuoka T, Momohara A, Sogo A, Takaso T, Peng C-I (2006) Phylogeography of the genus Cardiandra based on genetic variation in cpDNA sequences. Journal of Plant Research 119(4): 401–405. https://doi.org/10.1007/s10265-006-0283-1 (opens in a new tab)
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)