Hydrangea schlimii Briq. — Mophead sprawling hydrangea

Introduction

Few species in Hydrangea present a more intriguing unresolved problem than mophead sprawling hydrangea. Hydrangea schlimii is known from a single historical collection made around Ocaña in Norte de Santander, Colombia, about the middle of the nineteenth century. Despite subsequent botanical exploration, no modern population has been confidently relocated, no fresh material has been available for DNA analysis, and even its present existence in the wild is unknown (Samain et al. 2021).

What makes the surviving specimen extraordinary is its inflorescence. Cornidia typically bears numerous small reproductive flowers accompanied, in many species, by a limited number of flowers with enlarged petaloid sepals around or within the inflorescence. In the H. schlimii type, most of the flowers appear to possess enlarged sepals. The effect approaches the “mophead” architecture familiar from cultivated bigleaf hydrangeas but is essentially unknown as a normal species-level condition in Cornidia (Samain et al. 2021).

This creates an unusually difficult taxonomic choice. One possibility is that H. schlimii represents a genuine Colombian lineage in which enlarged floral displays evolved to an extreme degree. Another is that the only known specimen records a localized developmental mutation—essentially the wild equivalent of the mophead mutations repeatedly selected in cultivated hydrangeas. The 2021 revisers explicitly considered that possibility. Yet the leaves of the type could not be matched convincingly with any better-known species, preventing them from responsibly dismissing the name as a mutant individual of H. oerstedii, H. peruviana, or another Cornidia (Samain et al. 2021).

Tree TSAR therefore provisionally retains H. schlimii as a species, but with unusually high uncertainty. This is not a claim that the mophead phenotype has been demonstrated to define an evolutionary lineage. It is the more conservative position while the only available specimen simultaneously possesses unusual floral morphology and apparently distinctive foliage.

Rediscovery could resolve almost everything. If an Ocaña population proves to contain numerous plants with the same leaf morphology and the same inflorescence form, H. schlimii could emerge as one of the most biologically remarkable species in the genus. If ordinary lacecap-like individuals with identical vegetative morphology occur alongside occasional mopheads, the species hypothesis would need to be reassessed. A single living population could therefore change the interpretation dramatically.

Horticultural and Agricultural Uses

There is no documented horticultural history for H. schlimii, but its potential significance to horticulture is obvious. A naturally occurring Cornidia lineage consistently producing mophead-like inflorescences would represent an extraordinary independent development of the horticultural architecture so familiar in H. macrophylla.

That possibility should not be oversold while the taxon remains known only from its type. The most valuable horticultural action would currently be rediscovery and conservation, not commercialization. If plants are found, both apparently normal and mophead-like individuals should be documented and propagated separately, with precise provenance and reproductive status.

The developmental genetics could also be unusually informative. Comparison with cultivated mophead mutations in other Hydrangea lineages might reveal whether superficially similar inflorescences arose through homologous developmental pathways or entirely different mechanisms.

Conservation Concerns

Samain et al. (2021) treated H. schlimii as Data Deficient because both its taxonomic status and its conservation status remain unresolved. The species is known only from the Ocaña type locality and has apparently not been collected since about 1850.

Data Deficient is especially sobering here: the plant could be overlooked, extraordinarily localized, or extinct. The historical forests around Ocaña should be targeted for botanical survey using the leaf morphology of the type rather than searching solely for conspicuous mophead inflorescences, since a developmental mutation—if that hypothesis is correct—might not characterize every plant.

Plants of the World Online currently treats H. schlimii as a synonym of H. peruviana var. peruviana. That treatment suppresses precisely the unresolved biological question identified by the specialist revision (Royal Botanic Gardens, Kew 2026).

Additional Information

Open-access 2021 Hydrangea schlimii discussion (opens in a new tab): — includes an image of the historical specimen and the authors' explicit discussion of the possible mophead-mutation hypothesis.

iNaturalist observations for Hydrangea schlimii (opens in a new tab): — any credible modern observation near Ocaña would warrant close 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)

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 (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)