A botanical type is the element to which a scientific name is permanently linked, providing the reference point for determining what that name denotes. Historical type specimens can present obstacles to contemporary systematics because modern studies may require comparative morphology, population genetics, reproductive biology and other evidence that is difficult to apply to old material. The project therefore seeks “topotypic vouchers,” or newly collected specimens from a type locality, that can supplement original types without automatically replacing them. The researchers began with the 222-name checklist published by Chen and colleagues in 2021, examined the original descriptions associated with each name and searched historical literature, herbarium catalogues, Google Scholar, JSTOR and PteridoPortal for additional information and specimens.

Most of the early work focused on P, the herbarium of the Muséum national d’Histoire naturelle in Paris, where many Vietnamese types collected during the colonial period are deposited. Of the 250 recognized names, 194 have their types at P, and 185 were based on material collected by French botanists between 1837 and 1937. The researchers also assessed the principal collectors behind those names. Benjamin Balansa contributed material for 31 pteridophyte names, including 22 from Mount Ba Vì, during expeditions that yielded more than 5,600 specimens. Léopold Cadière supplied 23 type-based names, while Philippe Albert Eberhardt, who surveyed Tam Đảo and the Lang Biang Plateau, was represented by 33 taxa. Nineteen names were based on collections by Paul Alfred Pételot, chiefly in northern Vietnam, and 20 were based on material gathered by Eugène Poilane, who explored areas including Lai Châu, Ninh Thuận and Quảng Nam.

Mapping the historical collections exposed both the reach of colonial-era exploration and its limitations. Eight type specimens predated the 1850s, seven of them collected by Charles Gaudichaud-Beaupré in Đà Nẵng, formerly called Tourane. Only six types were collected during the wars and postwar period, all by Vietnamese botanists in northern Vietnam. More recent collecting has included species from less intensively explored provinces, such as Cyrtomium elongatum from Hà Giang, now part of Tuyên Quang Province, and Arachniodes longicaudata from Nghệ An. Apparent gaps around Điện Biên, Gia Lai and the Mekong Delta remain uncertain: they may reflect lower diversity or simply less botanical exploration. Because many original localities lack clear modern equivalents, the team consulted early twentieth-century maps, collector biographies and ecological information before georeferencing interpreted sites and displaying their distribution in R.

Three historical locality names received clearer modern interpretations. “Tonkin, Tu Phap,” where Balansa made abundant collections, refers to Thủ Pháp in present-day Sơn Tây Province along the Black River, now called the Sông Đà. The surrounding landscape has since been transformed by agriculture and settlement, so the forested western slope of the Ba Vì range was identified as an ecologically appropriate place to search for substitute topotypic material. Tourane was the former name for Đà Nẵng, where Gaudichaud-Beaupré collected six ferns that were later described from his material. The habitats associated with these collections in low- to mid-elevation primary forest are no longer present within the modern city, leaving remnants on the Sơn Trà Peninsula or in the Bà Nà Hills as potential search areas. “Taai Wong Mo Shan,” used by the Chinese collector Wai-Tak Tsang, was identified as a Cantonese rendering corresponding to Hoành Mô Commune in Quảng Ninh Province.

Among the 26 names whose original material was newly found, eight were at species rank and 18 at infraspecific rank. Most were provisionally interpreted as synonyms, often because the differences from typical varieties were slight and the available evidence was insufficient. Four names were treated tentatively as distinct species: Pteris parviloba, Pteris quadriaurita var. infurcata, Polystichum tonkinense and Asplenium eberhardtii. A specimen matching the protologue of Pteris quadriaurita var. parviloba was designated the lectotype. Collected by A. Billet in 1892 at Quảng Uyên, Cao Bằng, it corresponds to the date and locality stated when Christ and Billet published the taxon as a variety. The designation also resolves an earlier choice of a Chinese specimen that had not been cited in the protologue, while the accepted authorship of the species is “(Christ) Christ.”

The single specimen matching the protologue of Pteris quadriaurita var. infurcata was recognized as the holotype of a name based on Eberhardt’s collection from the Cú Bi River north of Huế. It contains three juvenile, sterile individuals, preventing a full assessment from the type alone. A later expedition to Quảng Nam Province, about 150 km south of the original site, found fertile material assigned to the same taxon. These plants exceed one metre in height and bear once-pinnate-pinnatifid fronds with up to three pairs of pinnae and broad pinnae reaching 5 cm across. The material is morphologically distinct from P. quadriaurita, an American species widely misapplied in Asia, but its relationship to similar taxa including P. longipinnula and P. clemensiae remains unresolved. The project also recognized the poorly preserved holotype of Polystichum tonkinense and the holotype of Asplenium eberhardtii, the latter requiring comparison with related Asian species.

For Trichomanes javanicum var. glabra, the project located all three syntypes cited by Bonaparte at P. Their morphology was consistent with Cephalomanes sumatranum following a recent revision of the genus, and the Cadière specimen from Thanh Tân was selected as lectotype because it consists of one individual with abundant fertile fronds. Two sheets labeled as Aspidium distans var. cadieri were also examined. Both belong to Tectaria kusukusensis, and one bears an annotation by Tardieu-Blot identifying that species, showing that its placement under Glaphyropteridopsis erubescens in a later flora was not a simple misidentification on that sheet. The project did not attempt broad lectotypification because such decisions are better made within comprehensive taxonomic revisions, but it resolved these two selected cases.

Côn Đảo provides a prominent example of the limits imposed by incomplete historical evidence. Schizaea dichotoma was the first pteridophyte described from Vietnam, although Linnaeus mistakenly listed China as its type locality. Historical research indicates that the correct locality was Cochinchina, an early name for southern Vietnam, and associates the relevant material with James Cunninghame, who worked at Pulo Condore in 1703. Molecular analysis has shown that the name historically applied across the Old World tropics is polyphyletic, leading to the separation of African, Madagascan and Mascarene populations as S. medusa. The Asian and Oceanian group remains internally unresolved. Two week-long expeditions in 2025 and 2026 surveyed coastal forests, rainforests and riversides on Côn Đảo, reaching nearly 550 metres above sea level, but did not locate S. dichotoma. The authors note that a very small population or local extinction is possible, while emphasizing that broader investigation is needed.

At Bà Nà, a mountain about 40 km west of Đà Nẵng, the project conducted a four-day expedition across forest types and elevations in August 2025. Botanical collecting there between 1920 and 1934 had produced 16 new pteridophyte taxa, and a colonial tourism station had been established in 1919. Today, a resort complex covers more than 200 hectares of the summit. The expedition found only eight of the historically recorded taxa, including some species newly reported for Vietnam and a potentially undescribed species that the authors say will be described separately. Several absences may involve unusual growth forms, such as a crested form of Blechnum orientale, rather than missing species. Others were more widespread in Vietnam or associated with mossy summit forest that no longer exists at Bà Nà, while Macrothelypteris banaensis, known only from its type collection, was not relocated. The case study illustrates how contemporary rediscovery efforts can document present distribution and habitat availability, but it does not by itself establish the cause of every absence or confirm global extinction.

Collectively, the results demonstrate how historical type material, biographical research and field surveys can expose gaps in the record of Vietnamese plant diversity. The project still faces substantial limitations: most Vietnamese specimens at P are only partly databased, the total size of its relevant holdings cannot yet be quantified, and preliminary morphological identifications require molecular, ecological or broader comparative work. The maps also show where collecting has been sparse, but absence of records is not proof of biological absence. Nevertheless, the recovered types and clarified localities provide a firmer foundation for future revisions, targeted comparison with living populations and assessments of where historical plants still persist. By treating museum labels as geographic records rather than merely catalog entries, the project connects nineteenth- and twentieth-century botanical collecting with twenty-first-century field science.

Subject of Research: Taxonomic documentation and topotype fieldwork for Vietnamese ferns and lycophytes

Article Title: Studies of Vietnamese pteridophyte flora 4: topotype project

Article References: Chen, C.-W., Rouhan, G., Dang, V. D., Luu, H. T., Do, V. T., Lu, T. N., Chao, Y.-S., Huang, Y.-M., & Chung, K.-F. (2026). Studies of Vietnamese pteridophyte flora 4: topotype project. PhytoKeys, 275, 115-132. https://doi.org/10.3897/phytokeys.275.194552

Image Credits: AI Generated

DOI: 10.3897/phytokeys.275.194552

Keywords: Vietnamese pteridophytes, topotype project, type specimens, fern taxonomy, lycophytes, herbarium P, Côn Đảo, Bà Nà, historical localities, biodiversity documentation, Studies, Vietnamese