Hydrangea asterolasia Diels — Costa Rican sprawling hydrangea

Introduction

Costa Rican sprawling hydrangea is a functionally dioecious woody climber of exceptionally wet Central and northern South American forests. Its most recognizable feature is its reddish to ferruginous stellate pubescence: the lower leaf surface bears scattered greyish, whitish, or reddish hairs, while the young branches and inflorescence axes characteristically carry more conspicuous reddish stellate hairs. The flowers are white to greenish cream, and enlarged marginal flowers are normally present, giving flowering plants a distinctly different appearance from such neighbors as H. diplostemona, in which enlarged marginal flowers are absent (Sutton 2025).

In Costa Rica the species has been recorded from very wet forest, rain forest, cloud forest, and oak forest from about 1,100 to 2,650 m, including primary forest as well as forest edges and some disturbed habitats. Ferruginous pubescence is particularly useful in identification because even individuals that become almost glabrous elsewhere generally retain reddish hairs somewhere on the inflorescence (Morales 2007).

Its geographic circumscription is much less secure than that straightforward description suggests. Costa Rican and Ecuadorian material provide the clearest modern anchor for H. asterolasia, whereas current Plants of the World Online extends the species through Panama and Colombia to Peru. Older Costa Rican literature likewise employed a Costa Rica-to-Peru concept. The modern Cornidia phylogeny, however, demonstrates enough internal structure to make simple acceptance of every record across that range premature (Royal Botanic Gardens, Kew 2026).

Granados Mendoza et al. (2021) recovered sampled H. asterolasia and plants identified as H. aff. asterolasia within Clade J, but not as one cleanly isolated species branch. Two accessions identified as H. asterolasia were successively related to one H. aff. asterolasia, while another affinis accession was allied to an undescribed entity designated H. sp. 5. Trees and Shrubs Online consequently describes H. asterolasia as probably representing a species complex.

That result does not justify immediate splitting. It does show that the name currently covers a morphological and geographic problem rather than a fully tested evolutionary unit. Type-anchored sampling from Costa Rica and Ecuador should be compared directly with plants from Panama, Colombia, and Peru before the broadest database distribution is treated as a single biological range.

Historical nomenclature adds another layer. In Costa Rica, the South American name H. jelskii was formerly misapplied to H. asterolasia; it is not a synonym of this species (Morales 2007). A second name, H. epiphytica C.V.Morton, has appeared in database synonymy, but its relationship to H. asterolasia remains insufficiently type-audited and is better left unresolved than presented as an established synonym. That caution is specifically important for this already unstable species complex.

Horticultural and Agricultural Uses

Unlike many tropical Cornidia, H. asterolasia has at least a small documented horticultural foothold. A collection made by Crûg Farm in the Cordillera de Talamanca, Costa Rica, in 2004 under accession BSWJ 10481 remains in cultivation. Trees and Shrubs Online illustrates that accession growing under protection in North Wales and considers the species worth experimenting with in exceptionally mild climates. An initial attempt to establish it outdoors at Tregrehan in Cornwall was unsuccessful (Sutton 2025).

Those experiences fit the biology of a plant from high-rainfall tropical montane forest. Its altitudinal habitat does not automatically imply tolerance of hard frost: relatively cool montane temperatures occur together with extremely high atmospheric humidity and comparatively equable seasonal conditions.

The cultivated Costa Rican accession is also scientifically important. Because the species may encompass several lineages, authenticated material tied to collection locality has substantially more value than an unprovenanced plant sold only under the species name.

Conservation Concerns

No species-wide formal IUCN assessment is established in the sources reviewed here. Plants of the World Online reports H. asterolasia as “Not Evaluated” in the Colombian plant catalogue, while also displaying a separate machine-generated extinction-risk prediction of “not threatened.” The latter is a predictive model, not an IUCN Red List assessment and should not be presented as one (Royal Botanic Gardens, Kew 2026).

More fundamentally, conservation status cannot be interpreted confidently until the taxonomic unit itself is better defined. A nominal range from Costa Rica to Peru appears reassuringly broad, but if the present concept contains several geographically restricted species, that apparent security could disappear quickly when the complex is resolved.

Conservation collections should therefore emphasize geographically documented sampling from the securely identifiable Costa Rican and Ecuadorian populations while avoiding the assumption that those accessions represent all material currently filed under the name.

Additional Information

Trees and Shrubs Online — Hydrangea species of Section Cornidia (opens in a new tab): provides the current horticultural account and highlights the unresolved species-complex problem.

Plants of the World Online — Hydrangea asterolasia (opens in a new tab): gives the broad current backbone distribution from Costa Rica to Peru; this range should be interpreted cautiously in light of the phylogenetic evidence.

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)

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)

Morales JF (2007) Hydrangeaceae. In: Hammel BE, Grayum MH, Herrera C, Zamora N (eds.) Manual de plantas de Costa Rica, vol. VI: Dicotiledóneas (Haloragaceae–Phytolaccaceae). Monographs in Systematic Botany from the Missouri Botanical Garden 111. Missouri Botanical Garden Press, St. Louis, pp. 18–21. https://www.researchgate.net/publication/273945180_Morales_J_F_2007_Hydrangeaceae_In_B_E_Hammel_M_Grayum_C_Herrera_N_Zamora_eds_Manual_of_Plants_of_Costa_Rica_vol_VI_Monogr_Syst_Bot_Missouri_Bot_Gard_111_18-21 (opens in a new tab)