Hydrangea nahaensis
Lacandon sprawling hydrangea
On this page
Introduction
Lacandon sprawling hydrangea is a giant functionally dioecious root-climber endemic to the Nahá-Metzabok protected landscape of the Lacandon Forest in Chiapas. Mature plants can reach about 50 m and are unusually variable in their canopy behavior: some climb into and branch above the crown of their host, while others remain in the lower canopy and eventually arch downward. Its leaves are ovate to elliptic or somewhat lanceolate, entire-margined, and conspicuously clothed beneath with yellowish, brownish, or reddish stellate hairs. The flowering shoots also have a distinctive developmental rhythm, continuing vegetative growth above the inflorescences through several pairs of leaves and cataphylls (Samain et al. 2019).
The species occupies an unusually localized but exceptionally humid forest environment at about 830–1,130 m. Its habitat forms an ecotone between cloud forest and tropical rainforest, with deep soils, persistent moisture, and north-facing sites strongly influenced by the Gulf of Mexico's humid air and winter nortes. The plants climb a variety of large forest trees, including Magnolia lacandonica, laurels, oaks, and Hedyosmum mexicanum (Samain et al. 2019).
The molecular result is one of the most interesting in the Mexican radiation. The only H. nahaensis accession sampled by Granados Mendoza et al. (2021) was embedded among H. breedlovei accessions. Taken literally, the limited gene tree makes H. breedlovei non-monophyletic. Yet the same investigators emphasized that the two species can readily be distinguished in the field by foliage, pubescence, inflorescences, and architecture. Tree TSAR therefore retains H. nahaensis as a species while treating its genomic relationship with H. breedlovei as incompletely resolved.
This apparent contradiction is really a useful example of what Cornidia teaches about species formation. Morphological and ecological differentiation need not wait for every ancestral allele to sort into mutually exclusive lineages. A genomic study incorporating many individuals from the Nahá population and geographically representative H. breedlovei would be far more informative than treating the placement of one specimen in two nuclear loci as a species boundary by itself.
Horticultural and Agricultural Uses
No established ornamental or agricultural use has been documented for H. nahaensis. Its principal value in cultivation would be as a conservation and research accession rather than a conventional garden introduction.
That distinction matters unusually strongly here. Samain et al. observed abundant runner shoots and noted that apparently separate stems could actually belong to interconnected plants. Ex situ collections should therefore record individual provenance carefully rather than assuming that numerous collected shoots necessarily represent equivalent genetic diversity. The species' functional dioecy adds another dimension: reproductive conservation ultimately requires representation of both sexual functions.
Conservation Concerns
The known population presents an unusual mixture of encouraging and alarming evidence. Samain et al. (2019) described H. nahaensis as the largest and healthiest Mexican Cornidia population encountered during their field work, with vigorous juvenile runners spreading toward new host trees. The habitat lies within a protected area and benefits from conservation efforts carried out jointly by the Nahá community and governmental conservation authorities.
At the same time, the species is known from only this tiny area. The authors applied IUCN criteria and assessed it as Critically Endangered, calculating an extent of occurrence only slightly above 8 km² and emphasizing the continuing danger from fire and habitat damage. They also cautioned that clonal interconnection through runners may mean the number of genetically independent individuals is considerably lower than a stem count would suggest; only one fertile female individual was observed during their work (Samain et al. 2019).
The Nahá community therefore occupies a central place in this species' story. H. nahaensis was named specifically in recognition of the community and its tradition of conserving the surrounding forest. Here, cultural stewardship, taxonomic discovery, and species conservation are unusually directly connected.
Additional Information
- Plants of the World Online — Hydrangea nahaensis (opens in a new tab): Plants of the World Online accepts H. nahaensis and records it as native to Chiapas.
- Trees and Shrubs Online — Section Cornidia (opens in a new tab): Trees and Shrubs Online provides a concise comparison with other Mexican Cornidia.
References and Further Reading
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)
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)