Hydrangea
Hydrangea
Synonyms
- Adamia
- Broussaisia
- Calyptranthe ()
- Cardiandra
- Cianitis
- Cornidia
- Decumaria
- Deinanthe
- Dichroa
- × Didrangea
- Heteromalla ()
- Hortensia
- Macnemaraea
- Pileostegia
- Platycrater
- Sarcostyles
- Schizophragma
- Forsythia [ ]
- Hydrangia [ ]
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Treatment and Overview
Hydrangea is the large and morphologically diverse flagship genus of the Hydrangea Family (Hydrangeaceae). Tree TSAR recognizes 111 non-hybrid living species, together with several named hybrids and accepted lower-rank entities. Most hydrangeas are familiar as deciduous or evergreen shrubs, but the genus also encompasses small trees, enormous root-climbing woody vines, perennial subshrubs, and genuinely herbaceous rhizomatous plants. That breadth is not an artifact of indiscriminate lumping. It reflects a modern phylogenetic understanding of Hydrangeeae in which plants once distributed among nine genera form a single evolutionary radiation best represented as a broadly circumscribed Hydrangea with substantial internal structure (De Smet et al. 2015; Yang et al. 2024).
The current Tree TSAR treatment is more inclusive at species rank than some global backbones. Plants of the World Online currently lists 98 accepted species under Hydrangea, whereas the Tree TSAR roster recognizes 111 non-hybrid species. The discrepancy reflects continuing differences in species delimitation, synonymy, and treatment of regional taxa rather than a major disagreement over the outer boundary of the genus. Species complexes in groups such as sect. Asperae, sect. Macrophyllae, and sect. Cornidia remain active areas of taxonomic research.
One genus from a collection of very different plants
The extraordinary variation within Hydrangea once appeared to support recognition of several separate genera. Broussaisia, Cardiandra, Decumaria, Deinanthe, Dichroa, Pileostegia, Platycrater, and Schizophragma were all maintained apart from a more narrowly defined Hydrangea. Molecular analyses demonstrated, however, that these lineages were nested among traditional hydrangeas, leaving Hydrangea sensu stricto extensively paraphyletic or polyphyletic when the satellite genera were retained. De Smet et al. (2015) therefore expanded Hydrangea to encompass the entire tribe Hydrangeeae and transferred much of the useful older generic structure to sectional rank.
A competing solution was proposed by Ohba and Akiyama (2016), who emphasized the conspicuous morphological and ecological differences among these lineages and divided broad Hydrangea into several genera, including Hortensia, Platycrater, Cornidia, Calyptranthe, and Heteromallae. Tree TSAR instead retains broad Hydrangea. The broad treatment resolves the demonstrated phylogenetic defect while allowing the same morphological and evolutionary diversity to be communicated through subgenera and sections. The most recent comprehensive phylogenomic treatment recovered five major clades and recognized five subgenera and 19 sections, providing a strong infrageneric framework without requiring renewed fragmentation of the genus (Yang et al. 2024).
This treatment also satisfies an important proportionality test. Many of the former genera remain excellent morphological concepts, but recognizing each at genus rank would convey little evolutionary information that cannot be retained more economically as infrageneric groups. The result is a genus whose diversity can initially seem surprising but becomes intelligible once its principal lineages are recognized.
Growth form: from woody climbers to rhizomatous herbs
Most Hydrangea species conform to Tree TSAR's Woody Tree, Shrub, or Vine growth-form category. This category includes not only the familiar erect shrubs and occasional small trees but also the climbing hydrangeas. Species derived from the former Decumaria, Pileostegia, and Schizophragma, together with the predominantly Neotropical sect. Cornidia, may climb high into forest canopies, but their persistent woody shoot systems make them architectural variants of the same basic woody growth form rather than a separate growth-form category. Some sect. Cornidia species are massive root climbers capable of ascending tens of metres through humid montane forest.
Subgenus Cardiandra marks a much deeper departure from that woody framework. Yang et al. (2024) recovered growth habit as one of the useful characters defining major infrageneric groups, with subshrub habit characteristic of sect. Cardiandra and herbaceous habit characteristic of sect. Deinanthe. Tree TSAR refines this distinction using perennial plant architecture. Members of sect. Cardiandra are treated as Perennial Subshrubs From Woody Bases: their enduring framework is woody or suffrutescent at or below the base, while the aerial shoots can behave much like those of herbaceous woodland perennials. This intermediate architecture helps explain why the same lineage has often been described as herbaceous in floristic and horticultural literature but as subshrubby in other treatments. The difference is substantially one of emphasis: seasonal appearance can resemble an herb, while the persistent perennial axis retains the woody character that separates the group from genuinely herbaceous hydrangeas.
Section Deinanthe carries that architectural reduction farther. Its two species, H. bifida and H. caerulea, are fundamentally herbaceous rhizomatous perennials whose aerial growth is renewed from persistent underground rhizomes rather than from a woody basal shoot framework. Tree TSAR therefore treats them as Perennial Root-Hardy Geophytes from Rhizomes. The contrast between sect. Cardiandra and sect. Deinanthe is consequently more precise than a simple division between “shrubs” and “herbs”: one lineage retains a reduced suffrutescent perennial framework, whereas the other has crossed into genuinely herbaceous rhizomatous geophytism.
Broad Hydrangea consequently spans three Tree TSAR growth-form categories: woody trees, shrubs, and vines; perennial subshrubs from woody bases; and rhizomatous perennial geophytes. The transition from a persistent woody framework through suffrutescent architecture to complete herbaceous shoot replacement is one of the clearest expressions of morphological diversification within the genus. It also provides a useful reminder that growth form can strongly diagnose internal lineages without necessarily defining generic boundaries.
Geography and evolutionary history
Hydrangea has a strikingly disjunct native distribution. Its greatest diversity lies in eastern and southeastern Asia, but native lineages also occur in Malesia, Hawaii, eastern and central North America, Mexico and Central America, and along the mountains of western South America. Plants of the World Online records a native range extending from China and the Kuril Islands through tropical Asia and the Hawaiian Islands, as well as from eastern North America southward into Central and South America.
Phylogenomic dating places the stem of Hydrangeeae at approximately 48.4 million years ago and the crown radiation at about 23 million years ago, near the Oligocene-Miocene transition. Its modern distribution developed through repeated episodes of dispersal, vicariance, climatic change, and regional isolation. Fossil and biogeographic evidence indicates that hydrangeas formerly occupied parts of the Northern Hemisphere from which they are now absent, helping explain the modern separation of major Asian and American centers of diversity (Yang et al. 2023).
This geographic history is reflected at much finer scales as well. Population and phylogenetic work in Japan, China, and the Neotropics has repeatedly uncovered lineage structure that was hidden beneath broadly interpreted morphological species. In sect. Asperae, molecular species-delimitation analyses have revealed both cryptic lineages and cases in which traditional morphotypes do not correspond cleanly to independently evolving units. Similar work in sect. Cornidia continues to uncover previously overlooked climbing species. The higher-level circumscription of Hydrangea is therefore much more stable than the boundaries of many of its constituent species (De Smet et al. 2017; Granados Mendoza et al. 2021).
Horticultural and Agricultural Uses
Few temperate woody genera have achieved the horticultural prominence of Hydrangea. Garden culture is dominated by a relatively small portion of the genus, especially H. macrophylla and its relatives, H. paniculata, H. arborescens, H. quercifolia, and a growing assortment of Asian species. Mophead and lacecap cultivars derived principally from the H. macrophylla complex established the popular image of a hydrangea, while breeding in H. paniculata and H. arborescens has greatly expanded the range of flower forms, plant sizes, and climatic tolerances available to gardeners.
Broad Hydrangea also reveals how incomplete that familiar horticultural image is. The former Schizophragma, Pileostegia, and Decumaria contribute spectacular woody climbers capable of covering trunks and large walls; less familiar Asian shrubs add foliage, indumentum, bark, and floral characters unlike those of common garden cultivars; and Subgenus Cardiandra extends the genus into the herbaceous perennial garden. The same phylogenetic breadth that once encouraged generic segregation thus provides horticulturists with growth forms ranging from large canopy vines to low rhizomatous woodland plants.
The famous relationship between soil conditions and flower color in H. macrophylla is also more chemically precise than the common maxim that acidic soil simply “turns hydrangeas blue.” Blue coloration depends on complexes involving delphinidin-derived anthocyanin pigments, copigments, and aluminum ions within the sepals. Soil acidity is important largely because it influences aluminum availability and uptake. Red, purple, and blue sepals are therefore alternative expressions of an interacting chemical system rather than direct color responses to soil pH alone (Yoshida et al. 2021).
Species diversity within the genus has become increasingly important to breeding. Wild taxa provide potential sources of cold hardiness, heat tolerance, disease resistance, reblooming behavior, plant architecture, and novel floral traits. At the same time, reproductive barriers, ploidy differences, and uneven cross-compatibility mean that horticultural relationships cannot be inferred simply from the ease with which species can be placed in the same genus. Broad Hydrangea is an evolutionary classification, not an assertion that all of its species are readily interfertile.
Conservation Issues
The extraordinary abundance of cultivated hydrangeas can give a misleading impression of security. Conservation concern is concentrated unevenly across the wild genus, particularly in narrowly endemic species, insular lineages, specialized montane habitats, and regions experiencing rapid forest loss.
Section Cornidia is especially instructive. Its species are predominantly root-climbing lianas of humid tropical and subtropical montane forests from Mexico through Central and South America, with one Asian lineage. Intensive fieldwork in Mexico and elsewhere has revealed substantial previously unrecognized diversity, including large climbing species that had escaped formal recognition despite their size. Mexican members studied by Samain and colleagues were threatened primarily by deforestation and land-use change, and later phylogenetic work demonstrated that the section contains considerably more evolutionary structure than older broad species concepts suggested (Samain et al. 2019; Granados Mendoza et al. 2021).
Taxonomic resolution is therefore directly relevant to conservation. A supposedly widespread species may prove to consist of several geographically restricted evolutionary units, radically changing the conservation significance of individual populations. Continued revision of sect. Cornidia illustrates how botanical exploration, species delimitation, and conservation assessment can become inseparable.
The herbaceous hydrangeas present a different conservation problem. Population-genomic work on the Deinanthe lineage found strong geographic structuring associated with climatic refugia, historical range contraction, and postglacial population history. Individual populations can therefore preserve distinct portions of the evolutionary history of these rhizomatous woodland plants. Conservation of the group requires attention not only to species survival but also to geographically structured genetic diversity (Sakaguchi et al. 2021).
Similar concerns recur elsewhere in Hydrangea: restricted island endemics, narrowly distributed Asian species, montane forest specialists, and newly separated members of difficult species complexes may each require conservation assessments that differ substantially from those of their widespread cultivated relatives. For a genus so familiar in gardens, substantial portions of its wild evolutionary diversity remain poorly represented in cultivation and incompletely studied in nature.
Infrageneric Groups
The current Tree TSAR classification follows the five-subgenus framework supported by Yang et al. (2024). These five subgenera contain 19 sections, preserving much of the morphological information once expressed through separate genera. Tree TSAR also standardizes common names for many infrageneric groups, particularly sections corresponding to lineages historically treated as genera, where established vernacular usage can be retained without obscuring the broader classification. This framework emphasizes the distinctiveness of the major lineages while keeping them within a phylogenetically coherent broad concept of Hydrangea.
Subgenus Decumaria contains sections Decumaria, Pileostegia, Schizophragma, and Sinenses. It contains several of the genus's best-developed woody climbing lineages, including plants historically familiar under the generic names Decumaria, Pileostegia, and Schizophragma.
Subgenus Heteromallae contains sect. Heteromallae. It is dominated by Asian woody shrubs and small trees and includes the lineage represented horticulturally by H. paniculata and its relatives.
Subgenus Cardiandra contains sections Cardiandra and Deinanthe. It represents the genus's most pronounced departure from ordinary woody architecture. Sect. Cardiandra consists of suffrutescent, rhizomatous plants treated by Tree TSAR as perennial subshrubs from woody bases, whereas sect. Deinanthe consists of genuinely herbaceous rhizomatous perennials. The contrast between these closely related growth strategies makes subg. Cardiandra one of the clearest demonstrations of architectural evolution within broad Hydrangea.
Subgenus Hydrangea contains sections Asperae, Calyptranthe, Cornidia, and Hydrangea. Its diversity ranges from familiar erect shrubs and North American species to temperate Asian climbers and the remarkable Neotropical canopy lianas of sect. Cornidia.
Subgenus Dichroa contains sections Broussaisia, Chinenses, Dichroa, Hirtae, Kawagoeanae, Kwangsienses, Macrophyllae, and Stylosae. It includes some of the genus's most familiar cultivated species, particularly the H. macrophylla complex, while also encompassing lineages once considered sufficiently distinctive to warrant separate generic recognition.
Together these groups reveal why modern Hydrangea is simultaneously broad and biologically coherent. Its major lineages are strongly differentiated in growth form, morphology, geography, and ecology, but those differences are better understood as the products of diversification within a single ancient radiation than as evidence that every distinctive branch requires a separate genus.
Accepted Taxa
| Hydrangea acuminata | Subgenus Dichroa | Section Macrophyllae | Siebold & Zucc. | Sour hydrangea |
| Hydrangea acuminata var. australis | Subgenus Dichroa | Section Macrophyllae | (T.Yamaz.) S.Fujii, Sh.Murak. & M.Maki | Southern sour hydrangea |
| Hydrangea acuminata var. yakushimensis | Subgenus Dichroa | Section Macrophyllae | (Yahara & Tagane) S.Fujii, Sh.Murak. & M.Maki | Yakushima sour hydrangea |
| Hydrangea × agricola | Subgenus Cardiandra | Section Cardiandra | (J.M.H.Shaw) J.M.H.Shaw | Crûg Farm herb hydrangea |
| Hydrangea albostellata | Subgenus Hydrangea | Section Cornidia | Samain, Najarro & E.Martínez | Downy sprawling hydrangea |
| Hydrangea alternifolia | Subgenus Cardiandra | Section Cardiandra | Siebold | Japanese herb hydrangea |
| Hydrangea × amagiana | Subgenus Dichroa | Intersectional Hybrids | Makino | Izu hydrangea |
| Hydrangea amamiohsimensis | Subgenus Cardiandra | Section Cardiandra | (Koidz.) Y.De Smet & C.Granados | Nansei herb hydrangea |
| Hydrangea ampla | Subgenus Decumaria | Section Schizophragma | (Chun) Y.De Smet & C.Granados | Windmill hydrangea vine |
| Hydrangea ampla Choufenianum Form | Subgenus Decumaria | Section Schizophragma | Choufen hydrangea vine | |
| Hydrangea ampla Megalocarpa Form | Subgenus Decumaria | Section Schizophragma | Giant-bract hydrangea vine | |
| Hydrangea anomala | Subgenus Hydrangea | Section Calyptranthe | D.Don | Chinese climbing hydrangea |
| Hydrangea arborescens | Subgenus Hydrangea | Section Hydrangea | L. | Smooth hydrangea |
| Hydrangea arguta | Subgenus Dichroa | Section Broussaisia | (Gaudich.) Y.De Smet & C.Granados | Kanawao hydrangea |
| Hydrangea aspera | Subgenus Hydrangea | Section Asperae | Buch.-Ham. ex D.Don | Roughleaf hydrangea |
| Hydrangea aspera ssp. robusta | Subgenus Hydrangea | Section Asperae | (Hook.f. & Thomson) E.M.McClint. | Tall hydrangea |
| Hydrangea asterolasia | Subgenus Hydrangea | Section Cornidia | Diels | Costa Rican sprawling hydrangea |
| Hydrangea barbara | Subgenus Decumaria | Section Decumaria | (L.) Bernd Schulz | Woodvamp hydrangea |
| Hydrangea bifida | Subgenus Cardiandra | Section Deinanthe | (Maxim.) Y.De Smet & C.Granados | Two-lobed herb hydrangea |
| Hydrangea breedlovei | Subgenus Hydrangea | Section Cornidia | Samain, Najarro & E.Martínez | Cloudforest sprawling hydrangea |
| Hydrangea bretschneideri | Subgenus Heteromallae | Section Heteromallae | Dippel | Mongolian hydrangea |
| Hydrangea caerulea | Subgenus Cardiandra | Section Deinanthe | (Stapf) Y.De Smet & C.Granados | Blue herb hydrangea |
| Hydrangea carroniae | Subgenus Hydrangea | Section Cornidia | Samain & E.Martínez | Veracruz sprawling hydrangea |
| Hydrangea caucana | Subgenus Hydrangea | Section Cornidia | Engl. | Gland-tooth sprawling hydrangea |
| Hydrangea chungii | Subgenus Dichroa | Section Chinenses | Rehder | Fujian hydrangea |
| Hydrangea cinerea | Subgenus Hydrangea | Section Hydrangea | Small | Ashy hydrangea |
| Hydrangea coenobialis | Subgenus Dichroa | Section Chinenses | Chun | Monastery hydrangea |
| Hydrangea corylifolia | Subgenus Decumaria | Section Schizophragma | (Chun) Y.De Smet & C.Granados | Hazel-leaf hydrangea vine |
| Hydrangea crassa | Subgenus Decumaria | Section Schizophragma | (Hand.-Mazz.) Y.De Smet & C.Granados | Leatherleaf hydrangea vine |
| Hydrangea crassa var. elliptica | Subgenus Decumaria | Section Schizophragma | J.Anthony [TSAR]* | Elliptic-leaf hydrangea vine |
| Hydrangea daimingshanensis | Subgenus Dichroa | Section Dichroa | (Y.C.Wu) Y.De Smet & C.Granados | Daimingshan bluebead hydrangea |
| Hydrangea davidii | Subgenus Dichroa | Section Hirtae | Franch. | David hydrangea |
| Hydrangea densifolia | Subgenus Cardiandra | Section Cardiandra | (C.F.Wei) Y.De Smet & C.Granados | Taiwanese herb hydrangea |
| Hydrangea diplostemona | Subgenus Hydrangea | Section Cornidia | (Donn.Sm.) Standl. | Shrubby sprawling hydrangea |
| Hydrangea durifolia | Subgenus Hydrangea | Section Cornidia | Briq. | Santander sprawling hydrangea |
| Hydrangea fauriei | Subgenus Decumaria | Section Schizophragma | (Hayata) Y.De Smet & C.Granados | Taiwanese hydrangea vine |
| Hydrangea febrifuga | Subgenus Dichroa | Section Dichroa | (Lour.) Y.De Smet & C.Granados | Common bluebead hydrangea |
| Hydrangea fistulosa | Subgenus Dichroa | Section Dichroa | (G.H.Huang & G.Hao) U.B.Deshmukh & M.B.Shende | Hollowstem bluebead hydrangea |
| Hydrangea glaucescens | Subgenus Decumaria | Section Schizophragma | (Rehder) Y.De Smet & C.Granados | Pale hydrangea vine |
| Hydrangea goudotii | Subgenus Hydrangea | Section Cornidia | Briq. | Columbian sprawling hydrangea |
| Hydrangea gracilis | Subgenus Dichroa | Section Chinenses | W.T.Wang & M.X.Nie | Slender hydrangea |
| Hydrangea grosseserrata | Subgenus Dichroa | Section Kawagoeanae | Engl. | Yakushima hydrangea |
| Hydrangea heteromalla | Subgenus Heteromallae | Section Heteromallae | D.Don | Woolly hydrangea |
| Hydrangea hirsuta | Subgenus Dichroa | Section Dichroa | (Gagnep.) Y.De Smet & C.Granados | Downy bluebead hydrangea |
| Hydrangea hirta | Subgenus Dichroa | Section Hirtae | (Thunb.) Siebold | Nettleleaf hydrangea |
| Hydrangea hwangii | Subgenus Dichroa | Section Dichroa | J.M.H.Shaw | Yunnan bluebead hydrangea |
| Hydrangea hydrangeoides | Subgenus Decumaria | Section Schizophragma | (Siebold & Zucc.) Bernd Schulz | Japanese hydrangea vine |
| Hydrangea hydrangeoides Concolor Form | Subgenus Decumaria | Section Schizophragma | Greenback hydrangea vine | |
| Hydrangea hydrangeoides Ulleungdo Form | Subgenus Decumaria | Section Schizophragma | Ulleung hydrangea vine | |
| Hydrangea hydrangeoides var. taquetii | Subgenus Decumaria | Section Schizophragma | (H.Lév.) J.M.H.Shaw | Jeju hydrangea vine |
| Hydrangea hydrangeoides var. yakushimensis | Subgenus Decumaria | Section Schizophragma | (J.M.H.Shaw) J.M.H.Shaw | Yakushima hydrangea vine |
| Hydrangea hypoglauca | Subgenus Heteromallae | Section Heteromallae | Rehder | Whiteback hydrangea |
| Hydrangea integrifolia | Subgenus Hydrangea | Section Cornidia | Hayata | Philippine sprawling hydrangea |
| Hydrangea involucrata | Subgenus Hydrangea | Section Asperae | Siebold | Bracted hydrangea |
| Hydrangea involucrata var. tokarensis | Subgenus Hydrangea | Section Asperae | M.Hotta & Shiuchi | Nansei bracted hydrangea |
| Hydrangea jelskii | Subgenus Hydrangea | Section Cornidia | Szyszyl. | Andean sprawling hydrangea |
| Hydrangea kawagoeana | Subgenus Dichroa | Section Kawagoeanae | Koidz. | Tokara hydrangea |
| Hydrangea kawakamii | Subgenus Hydrangea | Section Asperae | Hayata | Taiwan roughleaf hydrangea |
| Hydrangea kwangsiensis | Subgenus Dichroa | Section Kwangsienses | Hu | Guangxi hydrangea |
| Hydrangea kwangtungensis | Subgenus Dichroa | Section Hirtae | Merr. | Guangdong hydrangea |
| Hydrangea lalashanensis | Subgenus Dichroa | Section Chinenses | S.S.Ying | Lalashan hydrangea |
| Hydrangea lingii | Subgenus Dichroa | Section Chinenses | G.Hoo | Narrowleaf hydrangea |
| Hydrangea linkweiensis | Subgenus Dichroa | Section Chinenses | Chun | Lingui hydrangea |
| Hydrangea liukiuensis | Subgenus Dichroa | Section Dichroa | Nakai | Ryukyu bluebead hydrangea |
| Hydrangea lobbii | Subgenus Dichroa | Section Kawagoeanae | Maxim. | Philippine hydrangea |
| Hydrangea longifolia | Subgenus Hydrangea | Section Asperae | Hayata | Longleaf hydrangea |
| Hydrangea longipes | Subgenus Hydrangea | Section Asperae | Franch. | Longstalk hydrangea |
| Hydrangea luteovenosa | Subgenus Dichroa | Section Kawagoeanae | Koidz. | Sweet hydrangea |
| Hydrangea luteovenosa var. yakushimensis | Subgenus Dichroa | Section Kawagoeanae | (Masam.) Sugim. | Yakushima sweet hydrangea |
| Hydrangea macrocarpa | Subgenus Heteromallae | Section Heteromallae | Hand.-Mazz. | Silverback hydrangea |
| Hydrangea macrophylla | Subgenus Dichroa | Section Macrophyllae | (Thunb.) Ser. | Bigleaf hydrangea |
| Hydrangea macrosepala | Subgenus Dichroa | Section Kawagoeanae | Hayata | Large-sepal hydrangea |
| Hydrangea mangshanensis | Subgenus Dichroa | Section Chinenses | C.F.Wei | Mangshan hydrangea |
| Hydrangea marunoi | Subgenus Cardiandra | Section Cardiandra | Tagane & S.Fujii | Kimotsuki herb hydrangea |
| Hydrangea mathewsii | Subgenus Hydrangea | Section Cornidia | Briq. | Rusty sprawling hydrangea |
| Hydrangea medogensis | Subgenus Dichroa (provisional) | Section Chinenses (provisional) | X.Z.Lan, W.L.Zheng & W.Q.He | Medog hydrangea |
| Hydrangea minamitanii | Subgenus Dichroa | Section Macrophyllae | (H.Ohba) Yahara | Hyuga hydrangea |
| Hydrangea × mizushimarum | Subgenus Dichroa | Intersectional Hybrids | H.Ohba | Mizushima hydrangea |
| Hydrangea moellendorffii | Subgenus Cardiandra | Section Cardiandra | Hance | Chinese herb hydrangea |
| Hydrangea mollissima | Subgenus Dichroa | Section Dichroa | (Merr.) Y.De Smet & C.Granados | Hainan bluebead hydrangea |
| Hydrangea nahaensis | Subgenus Hydrangea | Section Cornidia | Samain & E.Martínez | Lacandon sprawling hydrangea |
| Hydrangea nebulicola | Subgenus Hydrangea | Section Cornidia | Nevling & Gómez Pompa | Mountain sprawling hydrangea |
| Hydrangea obtusifolia | Subgenus Decumaria | Section Sinenses | (Hu) Y.De Smet & C.Granados | Chinese scrambling hydrangea |
| Hydrangea oerstedii | Subgenus Hydrangea | Section Cornidia | Briq. | Ruby sprawling hydrangea |
| Hydrangea ofeliae | Subgenus Dichroa | Section Dichroa | Sodusta & Lumawag | Philippine bluebead hydrangea |
| Hydrangea otontepecensis | Subgenus Hydrangea | Section Cornidia | Samain & E.Martínez | Otontepec sprawling hydrangea |
| Hydrangea panamensis | Subgenus Hydrangea | Section Cornidia | Standl. | Panamanian sprawling hydrangea |
| Hydrangea paniculata | Subgenus Heteromallae | Section Heteromallae | Siebold | Panicle hydrangea |
| Hydrangea peruviana | Subgenus Hydrangea | Section Cornidia | Moric. ex Ser. | Ecuadorian sprawling hydrangea |
| Hydrangea petiolaris | Subgenus Hydrangea | Section Calyptranthe | Siebold & Zucc. | Japanese climbing hydrangea |
| Hydrangea pingtungensis | Subgenus Hydrangea | Section Calyptranthe | S.S.Ying | Pingtung climbing hydrangea |
| Hydrangea platyarguta | Subgenus Hydrangea | Section Asperae | Y.De Smet & C.Granados | Japanese tea hydrangea |
| Hydrangea pottingeri | Subgenus Dichroa | Section Chinenses | Prain | Chinese hydrangea |
| Hydrangea preslii | Subgenus Hydrangea | Section Cornidia | Briq. | Peruvian sprawling hydrangea |
| Hydrangea quercifolia | Subgenus Hydrangea | Section Hydrangea | W.Bartram | Oakleaf hydrangea |
| Hydrangea radiata | Subgenus Hydrangea | Section Hydrangea | Walter | Silverleaf hydrangea |
| Hydrangea sargentiana | Subgenus Hydrangea | Section Asperae | Rehder | Sargent hydrangea |
| Hydrangea scandens | Subgenus Dichroa | Section Kawagoeanae | (L.f.) Ser. | Deutzia hydrangea |
| Hydrangea schizomollis | Subgenus Decumaria | Section Schizophragma | Y.De Smet & C.Granados | Chinese hydrangea vine |
| Hydrangea schlimii | Subgenus Hydrangea | Section Cornidia | Briq. | Mophead sprawling hydrangea |
| Hydrangea seemannii | Subgenus Hydrangea | Section Cornidia | L.Riley | Mexican sprawling hydrangea |
| Hydrangea serrata | Subgenus Dichroa | Section Macrophyllae | (Thunb.) Ser. | Mountain hydrangea |
| Hydrangea serrata var. angustata | Subgenus Dichroa | Section Macrophyllae | (Franch. & Sav.) H.Ohba | Narrowleaf mountain hydrangea |
| Hydrangea serratifolia | Subgenus Hydrangea | Section Cornidia | (Hook. & Arn.) F.Phil. | Sawtooth sprawling hydrangea |
| Hydrangea sikokiana | Subgenus Hydrangea | Section Asperae | Maxim. | Shikoku hydrangea |
| Hydrangea sousae | Subgenus Hydrangea | Section Cornidia | Samain, Najarro & E.Martínez | Chiapas sprawling hydrangea |
| Hydrangea stenophylla | Subgenus Dichroa | Section Chinenses | Merr. & Chun | Willowleaf hydrangea |
| Hydrangea steyermarkii | Subgenus Hydrangea | Section Cornidia | Standl. | Tacaná sprawling hydrangea |
| Hydrangea strigosa | Subgenus Hydrangea | Section Asperae | Rehder | Late hydrangea |
| Hydrangea stylosa | Subgenus Dichroa | Section Stylosae | Hook.f. & Thomson | Himalayan hydrangea |
| Hydrangea sungpanensis | Subgenus Heteromallae | Section Heteromallae | Hand.-Mazz. | Songpan hydrangea |
| Hydrangea taiwaniana | Subgenus Hydrangea | Section Cornidia | Y.C.Liu & F.Y.Lu | Taiwan sprawling hydrangea |
| Hydrangea tapalapensis | Subgenus Hydrangea | Section Cornidia | Samain, Najarro & E.Martínez | Tapalapa sprawling hydrangea |
| Hydrangea tarapotensis | Subgenus Hydrangea | Section Cornidia | Briq. | Tarapoto sprawling hydrangea |
| Hydrangea tomentella | Subgenus Decumaria | Section Pileostegia | (Hand.-Mazz.) Y.De Smet & C.Granados | Rusty evergreen climbing hydrangea |
| Hydrangea trianae | Subgenus Hydrangea | Section Cornidia | Briq. | Leatherleaf sprawling hydrangea |
| Hydrangea × versicolor | Subgenus Dichroa | Intersectional Hybrids | (Fortune) J.M.H.Shaw | Sapphire hydrangea |
| Hydrangea viburnoides | Subgenus Decumaria | Section Pileostegia | (Hook.f. & Thomson) Y.De Smet & C.Granados | Chinese evergreen climbing hydrangea |
| Hydrangea villosa | Subgenus Hydrangea | Section Asperae | Rehder | Velvetleaf hydrangea |
| Hydrangea vinicolor | Subgenus Dichroa | Section Chinenses | Chun | Wineleaf hydrangea |
| Hydrangea wallichii | Subgenus Dichroa | Section Dichroa | J.M.H.Shaw | Himalayan bluebead hydrangea |
| Hydrangea weberbaueri | Subgenus Hydrangea | Section Cornidia | Engl. | Matapalo sprawling hydrangea |
| Hydrangea xanthoneura | Subgenus Heteromallae | Section Heteromallae | Diels | Nodding hydrangea |
| Hydrangea xinfeniae | Subgenus Dichroa | Section Dichroa | W.B.Ju & J.Ru | Xinfen bluebead hydrangea |
| Hydrangea yaoshanensis | Subgenus Dichroa | Section Dichroa | (Y.C.Wu) Y.De Smet & C.Granados | Luomeng bluebead hydrangea |
| Hydrangea yayeyamensis | Subgenus Dichroa | Section Kawagoeanae | Koidz. | Nansei hydrangea |
| Hydrangea yesoensis | Subgenus Dichroa | Section Macrophyllae | Koidz. | Hime hydrangea |
| Hydrangea × ytiensis | Subgenus Dichroa | Intersectional Hybrids | (J.M.H.Shaw) J.M.H.Shaw | Y Tý hydrangea |
| Hydrangea zhewanensis | Subgenus Dichroa (provisional) | Section Stylosae (provisional) | P.S.Hsu & X.P.Zhang | Zhejiang hydrangea |
Additional Information
- iNaturalist — Hydrangea (opens in a new tab): provides photographs and occurrence observations, although cultivated records can obscure native distributions.
- Trees and Shrubs Online — Hydrangea (opens in a new tab): provides extensive horticultural coverage and a particularly useful comparison between traditional generic concepts and broad Hydrangea.
- Plants of the World Online — Hydrangea (opens in a new tab): provides Kew's current accepted-name and distribution backbone.
- World Flora Online — Hydrangea (opens in a new tab): provides taxonomic and nomenclatural cross-referencing.
- International Plant Names Index — Hydrangea (opens in a new tab): provides nomenclatural publication data.
- Flora of China — Hydrangea and allied traditional genera (opens in a new tab): remains valuable for morphology and regional identification, although it predates the modern broad circumscription in places.
- GBIF — Hydrangea (opens in a new tab): provides occurrence data that should be interpreted cautiously for widely cultivated species.
References and Further Reading
De Smet Y, De Clerck O, Uemachi T, Granados Mendoza C, Wanke S, Goetghebeur P, Samain M-S (2017) Multilocus coalescent species delimitation to evaluate traditionally defined morphotypes in Hydrangea sect. Asperae (Hydrangeaceae). Molecular Phylogenetics and Evolution 114: 415–425. https://doi.org/10.1016/j.ympev.2017.05.021 (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)
Granados Mendoza C, Martínez Salas EM, Goetghebeur P, Wanke S, Samain M-S (2021) Molecular phylogeny, character evolution, and biogeography of Hydrangea section Cornidia, Hydrangeaceae. Frontiers in Plant Science 12: 661522. https://doi.org/10.3389/fpls.2021.661522 (opens in a new tab)
McClintock E (1957) A monograph of the genus Hydrangea. Proceedings of the California Academy of Sciences, Fourth Series 29(5): 147–256. https://www.biodiversitylibrary.org/part/51707 (opens in a new tab) https://doi.org/10.5281/zenodo.15905786 (opens in a new tab)
Ohba H, Akiyama S (2016) Generic segregation of some sections and subsections of the genus Hydrangea (Hydrangeaceae). Journal of Japanese Botany 91(6): 345–350. https://doi.org/10.51033/jjapbot.91_6_10703 (opens in a new tab)
Sakaguchi S, Asaoka Y, Takahashi D, Isagi Y, Imai R, Nagano AJ, Qiu Y-X, Li P, Lu R, Setoguchi H (2021) Inferring historical survivals of climate relicts: The effects of climate changes, geography, and population-specific factors on herbaceous hydrangeas. Heredity 126(4): 615–629. https://doi.org/10.1038/s41437-020-00396-4 (opens in a new tab)
Samain M-S, Hernández Najarro F, Martínez Salas EM (2019) The climbing hydrangeas (Hydrangeaceae) of Mexico, including description of six (critically) endangered new species. Acta Botanica Mexicana 126: e1463. https://doi.org/10.21829/abm126.2019.1463 (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)
Yang X, Zhang X, Xue T, Zhang X, Yang F, Yu J, Janssens SB, Bussmann RW, Yu S (2023) Phylogenomics and historical biogeography of Hydrangeeae (Hydrangeaceae) elucidate the effects of geologic and climatic dynamics on diversification. Proceedings of the Royal Society B: Biological Sciences 290(2003): 20230659. https://doi.org/10.1098/rspb.2023.0659 (opens in a new tab)
Yoshida K, Oyama K, Kondo T (2021) Insight into chemical mechanisms of sepal color development and variation in hydrangea. Proceedings of the Japan Academy, Series B 97(2): 51–68. https://doi.org/10.2183/pjab.97.003 (opens in a new tab)