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Hydrangea durifolia Briq.

Santander sprawling hydrangea

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Introduction

Santander sprawling hydrangea may be the most tantalizingly incomplete species in this entire revision complex. It is a northern Colombian Cornidia known with confidence from extraordinarily little material: the type from the Pamplona region of Norte de Santander and essentially one additional well-supported collection from the vicinity of La Baja in Santander, gathered in 1927 at about 3,000 m. No modern population has yet been relocated and no fresh tissue has been available for molecular analysis (Samain et al. 2021).

That scarcity creates a problem more subtle than simply having too few specimens. Much of the historical material consists of flowering branches whose leaves are borne along the inflorescence axis. Samain et al. (2021) emphasized that these can differ substantially from ordinary vegetative leaves and may lack the species-specific characters that make Cornidia identifiable. In their experience, isolated inflorescences could often be named confidently only after extensive familiarity with a species. The one additional H. durifolia specimen preserving ordinary vegetative foliage is therefore disproportionately important to the modern interpretation of the taxon.

What can be recovered from the surviving material suggests a real species rather than a nomenclatural ghost. Hydrangea durifolia is morphologically closest to H. oerstedii, but the former has conspicuously more coriaceous leaves, compact rather than lax cymes, inflorescences less than roughly 10 cm wide, and enlarged marginal sepals that are substantially smaller, thicker, and less papery. Briquet recognized these differences in 1919, and modern examination of the type material confirmed them (Samain et al. 2021; Sutton 2025).

The crucial point is what the evidence does not allow us to say. There are not enough specimens to describe the full range of variation, establish a modern distribution, determine whether the historic localities belong to one surviving population system, or test whether the apparent morphology is genetically independent from H. oerstedii. But neither did the revisers find evidence that justified collapsing H. durifolia into another species. Tree TSAR therefore retains it provisionally rather than converting absence of modern information into evidence of synonymy.

That makes H. durifolia an excellent example of an intellectually honest provisional species: not strongly corroborated, but supported by enough type-anchored differentiation that synonymization would presently require as much assumption as recognition. Rediscovery, rather than further rearrangement of old herbarium labels, is what is needed to resolve it.

Horticultural and Agricultural Uses

There is no meaningful horticultural history for H. durifolia. No authenticated living collection appears to have been studied, and its ecological requirements remain inferential.

The known Santander material came from very high elevation by Cornidia standards, around 3,000 m, raising obvious questions about cold tolerance. It would be premature, however, to translate Andean elevation directly into temperate-garden hardiness. Tropical high-elevation plants experience very different seasonal temperature and moisture regimes from those of continental temperate gardens.

For botanical gardens, an authenticated rediscovery would be exceptionally valuable. A living plant could answer questions that the surviving specimens cannot: whether the leathery foliage is consistent throughout development, how large the liana becomes, whether its small inflorescences remain stable across both sexes, and whether H. durifolia truly occupies an ecological niche distinct from H. oerstedii.

Conservation Concerns

The 2021 revision calculated an area of occupancy of only about 8 km² and noted that, if the known records accurately represented the living species, Critically Endangered could be plausible under IUCN criteria. The authors nevertheless chose Data Deficient, because neither its current distribution nor even the full limits of the taxon can be established from the surviving evidence (Samain et al. 2021).

That is the appropriate distinction. Data Deficient does not mean secure; here it means that the species could range from overlooked to nearly or already extinct, and the available information cannot discriminate between those possibilities.

Field work around Pamplona and the historic La Baja locality is therefore a priority. Rediscovery should be followed by collection of complete branches containing ordinary vegetative foliage, reproductive material from both sexes where possible, photographs of whole-plant architecture, and tissue suitable for nuclear genomic comparison.

Plants of the World Online currently places H. durifolia in synonymy beneath H. peruviana var. peruviana. That treatment predates incorporation of the biological distinctions emphasized by the 2021 revision and should not be interpreted as evidence that the species has subsequently been disproven (Royal Botanic Gardens, Kew 2026).

Additional Information

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

Samain M-S, Granados Mendoza C, Martínez Salas EM (2021) On Hydrangea peruviana, an endangered species from Ecuador, and Hydrangea oerstedii, very common in Costa Rica and Panama, and seven threatened Central and South American hydrangeas, which have been confounded with these. PhytoKeys 171: 91–153. https://doi.org/10.3897/phytokeys.171.56351

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/