The genus Argyreia, established by the Portuguese botanist João de Loureiro in 1790, belongs to the family Convolvulaceae, the same family as morning glories and sweet potatoes. It is distinguished chiefly by its indehiscent fleshy or mealy berries, fruits that do not split open at maturity, and it is distributed across continental Asia, from Southeast Asia and the Indian Subcontinent to China. Today, approximately 144 species are accepted worldwide, and recent taxonomic and nomenclatural work has sharpened the circumscription and typification of many of them. Yet several names described from Indochina in the early twentieth century, including the two species treated in the new paper, remained inadequately typified.

The problem stems from how early twentieth-century botanists described species. Gagnepain’s 1915 descriptions, published in the journal Notulae Systematicae in Paris, were based not on a single specimen but on multiple gatherings. For Argyreia laotica, the original material consisted of three gatherings collected by Massie, Dupuy and Thorel; for Argyreia mekongensis, three gatherings by Thorel and by the plant explorer Pierre. When a name is based on several specimens without one being singled out, all of them are technically syntypes, and the name’s meaning remains fluid until one specimen is formally chosen as the lectotype under the International Code of Nomenclature for algae, fungi, and plants.

Fixing that anchor matters for a practical reason: if different botanists choose different specimens as the type, the name could end up applied to different plants, rippling through checklists, conservation assessments and floristic inventories. Article 9.3 of the Code governs lectotypification, the process by which a lectotype is selected from among the syntypes to fix the application of a name permanently. The authors of the new study examined all the available original material before making their choice, weighing both the historical connection to the original description and the physical quality of the specimens themselves.

Tracking down that original material required an international digital detective effort. The researchers consulted high-resolution images through JSTOR Global Plants and the digitized collections of several major European herbaria: the Muséum National d’Histoire Naturelle in Paris, the Royal Botanic Garden Edinburgh, the Natural History Museum in London, the Royal Botanic Gardens at Kew, and the Conservatoire et Jardin botaniques de Genève. Nomenclatural information was cross-checked against the International Plant Names Index, Plants of the World Online and Tropicos. Crucially, the authors distinguished between specimens that genuinely belong to the original material and those that merely resemble the description, a distinction the Code requires: a specimen’s status as original material depends on its documented connection to the protologue, not on how complete or diagnostic it looks.

For Argyreia laotica, seven extant syntype specimens survive, all preserved in Paris. They represent the three gatherings cited by Gagnepain: Thorel 3286, Massie s.n. and Dupuy 117. The gathering Thorel 3286 proved especially significant because it carries the clearest geographical link to the original description. Its two surviving specimens bear labels reading Kemmarath and Vien-thian, localities explicitly cited in the 1915 protologue. The researchers selected the Paris specimen P00392012, labeled from Kemmarath, as the lectotype, because it preserves sufficient vegetative and reproductive material to support identification, and its duplicate P00392013 becomes the isolectotype.

Argyreia mekongensis presented a different challenge. While seven syntype specimens of the laotica complex survive in Paris, the original specimens of mekongensis held at Paris could not be located, a fate not uncommon for material cited in early twentieth-century publications. The surviving syntypes are scattered across European herbaria: Thorel 2150 from Stung-Treng in Cambodia is represented at London, Edinburgh and Kew, while two Pierre gatherings from Cochinchine, in what is now southern Vietnam, are held in Edinburgh, Geneva and Kew. The collector names, numbers and locality details on these sheets all match the gatherings cited in the protologue, confirming their status as original material.

The lectotype chosen for Argyreia mekongensis is the Edinburgh specimen E00273906, part of the Pierre 2 gathering collected near Baria, Bao-chiang and Gia-lau-me in Cochinchine. This gathering was singled out because it originates from the locality cited in the protologue and represents the most complete original material available. Among the examined specimens, the Edinburgh sheet preserves abundant vegetative and reproductive material and displays the widest range of diagnostic characters, including leaf morphology, indumentum, inflorescence structure and floral features. Duplicates of the same gathering in Geneva and at Kew become isolectotypes, and the remaining syntypes, including Pierre 10 at Kew and Thorel 2150 at three institutions, retain their status as original material.

The wider story here is the ongoing effort to bring order to the nomenclature of Indochinese plants, a region whose flora was documented largely by French expeditions in the nineteenth and early twentieth centuries. Collectors such as Thorel, who traveled with the Mekong expedition, and Pierre, whose Cochinchinese collections were foundational for Vietnamese botany, left behind herbarium sheets that are still being reconciled with the names they generated. Recent studies have also reshuffled Argyreia itself: both species treated here have at times been transferred to other genera, with laotica and mekongensis placed in Ipomoea in a 2019 treatment, and mekongensis earlier placed in Lettsomia. Stable types are essential groundwork for evaluating such competing classifications, because a name can only be applied or reassigned if the specimen anchoring it is unambiguous.

For working botanists, the practical payoff is immediate. Field biologists documenting the floras of Laos, Vietnam, Cambodia and neighboring countries can now check their material against a single, definitively designated specimen for each name, rather than a loose set of seven scattered sheets. The study, published in PhytoKeys, is part of a broader wave of typification work that continues to uncover how much of early tropical botany still rests on unexamined assumptions. With lectotypes now fixed for both Argyreia laotica and Argyreia mekongensis, two century-old names from the Mekong region finally have a firm and permanent foundation in the herbarium world.

Subject of Research: Lectotypification of two Indochinese Convolvulaceae species

Article Title: Lectotypification of Argyreia laotica Gagnep. and A. mekongensis Gagnep. & Courchet ( Convolvulaceae )

Article References: Lectotypification of Argyreia laotica Gagnep. and A. mekongensis Gagnep. & Courchet ( Convolvulaceae ). (n.d.). https://doi.org/10.3897/phytokeys.280.206333

Image Credits: AI Generated

DOI: 10.3897/phytokeys.280.206333

Keywords: Argyreia, Convolvulaceae, lectotypification, nomenclature, taxonomic types, Indochina, herbaria, PhytoKeys, plant taxonomy, Laos, Vietnam, botanical history