Hydrangea tarapotensis
Tarapoto sprawling hydrangea
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Introduction
Tarapoto sprawling hydrangea is a functionally dioecious Andean root-climbing liana distributed from Ecuador through Peru into eastern Bolivia. It produces branched, usually thyrse-like inflorescences of small pale flowers without enlarged marginal flowers. Its leaves are notably glabrous on both surfaces, while the branchlets and inflorescence branches bear stellate hairs—a simple but useful contrast with the hairy lower leaf surfaces of H. jelskii and the rugose, vein-hairy foliage of H. mathewsii (McClintock 1957; Granados Mendoza et al. 2021; Sutton 2025).
Ecological records provide a richer picture than its sparse online presence suggests. In the Maquipucuna cloud forests of Ecuador, collections identified as H. tarapotensis were made in primary forest between approximately 1,250 and 2,000 m and described as climbers with entire leaves and yellow-green flowers. Ecuadorian herbarium records also include a collection from about 3,000 m in Loja and, remarkably, a 2025 specimen from secondary humid forest near Archidona at approximately 814 m. Taken together, these records suggest appreciable elevational breadth, although their identification would benefit from renewed scrutiny as the Cornidia revision progresses (Webster & Rhode 2001).
Its name derives from Tarapoto in northern Peru and was published by Briquet in 1919. Major modern backbones currently accept the species across Ecuador, Peru, and Bolivia but also place the Colombian H. antioquiensis and Bolivian H. bangii in its synonymy. Plants of the World Online (opens in a new tab) That broad nomenclatural treatment now looks much less secure than the identity of H. tarapotensis itself.
Molecularly, this species is exceptional. Among the many Cornidia taxa represented by more than one accession in Granados Mendoza et al. (2021), only three morphologically defined species achieved strong species-level monophyly: H. serratifolia, H. panamensis, and H. tarapotensis. All sampled H. tarapotensis accessions clustered together with 100% bootstrap support within Clade F.
That result is especially striking because Clade F around it is otherwise extraordinarily messy. H. jelskii and H. mathewsii intermingle with one another and with unnamed entities, yet H. tarapotensis emerges from that same shallow radiation as a clean, strongly supported molecular lineage. Its glabrous leaves and distinct flowering morphology therefore correspond to a genomic signal much more clearly than do several neighboring traditional species.
The irony is that the strongest part of the species concept may currently be obscured by excessive synonymy. Granados Mendoza et al. directly compared the type specimens of H. tarapotensis, H. antioquiensis, and H. bangii. They reported that the Colombian and Bolivian types are readily distinguishable from true H. tarapotensis by both leaf and inflorescence morphology. Neither could be sampled molecularly because material of adequate DNA quality was unavailable (Granados Mendoza et al. 2021).
Consequently, H. antioquiensis and H. bangii should not yet be presented either as demonstrated synonyms or as fully restored species. They are probable resurrection candidates whose morphology already challenges the present backbone treatment but whose independent evolutionary status still needs fresh or topotypic material. This distinction is important. Strong monophyly of sampled H. tarapotensis actually strengthens the case for asking whether morphologically divergent Colombian and Bolivian plants fall outside that lineage.
A future study therefore has an unusually clean hypothesis to test. Sample plants matching the types of H. antioquiensis in Colombia and H. bangii in Bolivia and ask whether they fall inside the tightly coherent H. tarapotensis lineage. If they do, the molecular result would reveal remarkable morphological variation within one species; if they do not, two historically synonymized Andean hydrangeas would immediately become compelling candidates for reinstatement.
Horticultural and Agricultural Uses
No established horticultural trade in authenticated H. tarapotensis is documented. Its entire, glabrous foliage and branched white to yellow-green inflorescences are subtler than the conspicuous marginal-flowered displays of several other Cornidia, so its primary value in cultivation would presently be botanical rather than commercial.
Its apparent occurrence across a substantial elevational range makes provenance particularly interesting. Material originating around 3,000 m in southern Ecuador could differ substantially in climatic tolerance from lower-elevation populations, but there are presently no controlled trials allowing those differences to be translated into hardiness recommendations.
Living accessions would also be unusually useful taxonomically. Because sampled H. tarapotensis already forms a strong molecular reference lineage, authenticated cultivated plants could serve as a morphological comparison set against future collections of H. antioquiensis and H. bangii.
Conservation Concerns
No formal IUCN Red List assessment for H. tarapotensis was located in the sources reviewed. POWO's accepted distribution spans Ecuador, Peru, and Bolivia, which is appreciably broader than many threatened Cornidia endemics (Royal Botanic Gardens, Kew 2026).
The unresolved synonymy nevertheless affects interpretation of that range. If some records from Colombia or Bolivia historically attributed to broad H. tarapotensis actually represent H. antioquiensis or H. bangii, the range of the strongly supported biological lineage may differ from database maps. Conversely, the confirmed molecular samples already show that genuine H. tarapotensis itself is not merely a single-locality Tarapoto endemic.
Forest habitat remains relevant even where the species proves relatively widespread. Cornidia are persistent root-climbing lianas dependent on forest structure, and the section-wide synthesis emphasizes their strong association with humid primary forest, although individual species can occasionally persist in secondary habitats. The recent Ecuadorian collection from secondary humid forest is therefore encouraging but should not be generalized into broad disturbance tolerance (Sutton 2025).
Additional Information
- Plants of the World Online — Hydrangea tarapotensis (opens in a new tab): accepts the species from Ecuador to Bolivia but currently places H. antioquiensis and H. bangii in synonymy.
- Trees and Shrubs Online — Section Cornidia (opens in a new tab): summarizes its glabrous foliage, branched inflorescences, functional dioecy, and modern taxonomic context.
- iNaturalist observations — Hydrangea tarapotensis (opens in a new tab): may be useful for locating modern records, but observations from regions associated with H. antioquiensis or H. bangii deserve particular scrutiny.
References and Further Reading
Briquet JI (1919) Decades plantarum novarum vel minus cognitarum: Decades 17–25. Annuaire du Conservatoire et du jardin botaniques de Genève 20: 342–427. https://www.biodiversitylibrary.org/item/112421 (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)
Sutton J (2025) Hydrangea species of Section Cornidia. Trees and Shrubs Online. International Dendrology Society. https://www.treesandshrubsonline.org/articles/hydrangea/hydrangea-species-of-section-cornidia/ (opens in a new tab)
Webster GL, Rhode RM (2001) Plant diversity of an Andean cloud forest: Inventory of the vascular flora of Maquipucuna, Ecuador. University of California Press, Berkeley. https://doi.org/10.1525/california/9780520098305.001.0001 (opens in a new tab) https://www.amazon.com/dp/0520098307 (opens in a new tab)