Hydrangea preslii
Peruvian sprawling hydrangea
Synonyms
- Sarcostyles peruviana []
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Introduction
Peruvian sprawling hydrangea occupies an unusual place in the history of Cornidia. The name has traditionally been applied to a widespread functionally dioecious root-climbing hydrangea with simple, approximately umbel-like inflorescences, white flowers, no enlarged marginal flowers, entire leaf margins, and simple to stellate hairs on the branchlets and flowering axes. Yet almost every part of that apparently straightforward description is now shadowed by a deeper taxonomic question: how much of what botanists have called H. preslii actually belongs to this species? (McClintock 1957; Granados Mendoza et al. 2021; Sutton 2025).
The name is nomenclaturally anchored by Sarcostyles peruviana C.Presl ex DC., which is based on the same type and is therefore a secure homotypic synonym. Hydrangea preslii is also historically entangled with the very identity of Cornidia: Cornidia umbellata Ruiz & Pav. is the type species of the former genus Cornidia, and modern treatments have commonly placed that name in the synonymy of H. preslii. Because the biological circumscription of H. preslii is now being narrowed, however, the type of C. umbellata deserves direct renewed comparison before that historical synonymy is treated as biologically unquestionable (Samain et al. 2019).
The twentieth-century concept became extraordinarily inclusive. Current POWO still treats H. briquetii, H. ecuadorensis, H. inornata, H. sprucei, Cornidia umbellata, and Hydrangea umbellata beneath H. preslii, producing a nominal distribution from Costa Rica and Panama through Colombia and Ecuador to Peru and Bolivia. Plants of the World Online (opens in a new tab) That concept is increasingly difficult to reconcile with the specialist molecular and morphological evidence.
The most decisive case involves H. sprucei. Eight samples identified by Cornidia specialists as H. sprucei were included in Granados Mendoza et al. (2021). They did not cluster with the sampled H. preslii. Instead, all eight occurred in Clade G, where two separate sprucei groups were recovered, including one four-accession clade with 100% bootstrap support. The sampled H. preslii, meanwhile, lies in Clade E. A name traditionally buried inside H. preslii is therefore represented by multiple samples in a different major portion of the nuclear tree.
That makes H. sprucei the strongest current candidate for resurrection from the traditional preslii synonymy. It would nevertheless be premature to establish a separate treatment solely from the unpublished species-level revision: the sampled sprucei material itself occupies two sublineages, so the historical morphotype may conceal more than one species. Formal resurrection should follow a published, type-anchored circumscription rather than merely moving every specimen carrying the old name into a new page.
The briquetii–ecuadorensis–preslii problem is different. In Clade E, the single sampled H. preslii occurs with specimens identified by specialists as H. briquetii and H. ecuadorensis, an unnamed Hydrangea sp. 2, and another problematic morphotype. Unlike H. sprucei, these entities show only shallow separation in the available two-gene tree. The specialists nevertheless continued to distinguish H. briquetii and H. ecuadorensis morphologically rather than treating their old synonymy as settled (Granados Mendoza et al. 2021).
The most defensible present treatment is consequently a narrow, type-anchored H. preslii accompanied by an explicit unresolved species complex. H. briquetii and H. ecuadorensis are strong candidates for recognition but await a published circumscription; H. sprucei is an even stronger resurrection candidate because its sampled material lies outside Clade E entirely; and H. inornata still requires direct type study. None should simply be copied into the synonym list of H. preslii as though the twentieth-century broad concept had survived modern testing.
There is a fascinating practical indication of just how heterogeneous that old concept may be. Ecuadorian herbarium records labelled H. preslii extend from lowland Amazonian primary forest at approximately 240–480 m to wet montane forest close to 3,000–3,100 m. Some records come from Yasuní and lowland Pastaza, others from Andean forests around Baeza and Podocarpus National Park. These records cannot simply be assumed to represent the narrow species; instead, their enormous ecological span is precisely the kind of pattern that now warrants specimen-level re-identification against H. preslii, H. briquetii, H. ecuadorensis, H. sprucei, and unnamed Cornidia. Bndb (opens in a new tab)
Horticultural and Agricultural Uses
No securely documented ornamental tradition can presently be assigned to narrow H. preslii. Plants circulating under the old broad name would require voucher or provenance review before they could be used to characterize this species horticulturally.
The species complex is nevertheless highly relevant to botanical collections. Living plants collected with vouchers could supply precisely the features most difficult to recover from herbarium material: architecture, reproductive sex, leaf variation between extension and flowering shoots, inflorescence development, phenology, and ecological tolerances.
Conservation Concerns
Hydrangea preslii is formally listed as Least Concern on the IUCN Red List; Kew's current account links the 2021 assessment directly. Plants of the World Online (opens in a new tab) That formal status needs an unusually prominent taxonomic qualification in this treatment.
The assessment was made under the broad prevailing concept of H. preslii, for which current backbones still report a range from Costa Rica to Bolivia and synonymize multiple historical species. Plants of the World Online (opens in a new tab) The nuclear evidence now shows that at least H. sprucei-identified material belongs elsewhere in the Cornidia phylogeny, while H. briquetii and H. ecuadorensis remain morphologically differentiated entities within an unresolved complex. The geographic distribution and population count used for broad H. preslii therefore cannot automatically be transferred to a narrower biological species.
This does not mean that H. preslii is demonstrably threatened; it means that its current LC assessment and its present taxonomic circumscription are not perfectly aligned. Once the complex is revised, each resulting species—including narrow H. preslii—will require conservation assessment against its own distribution.
The problem provides an excellent illustration of taxonomic inflation working in reverse: over-lumping can make several restricted species appear collectively secure because their records are pooled beneath one widespread name.
Additional Information
- Plants of the World Online — Hydrangea preslii (opens in a new tab): shows the current broad backbone circumscription and its extensive synonymy; these should not be copied uncritically into the narrow species concept.
- Trees and Shrubs Online — Section Cornidia (opens in a new tab): explicitly identifies the preslii–briquetii–ecuadorensis assemblage as an unresolved species complex.
- iNaturalist observations — Hydrangea preslii (opens in a new tab): should be interpreted especially cautiously because observations may follow the much broader backbone concept.
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)
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)
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)