Takenoshin Nakai swallow-wort (Vincetoxicum nakaianum) replaces V. magnificum and C. magnificum

NEWS - Researchers reported an erect herbaceous species distributed in the eastern part of Honshu Island, Vincetoxicum magnificum (Nakai) Kitag. based on Cynanchum magnificum Nakai, nomen nudum. Therefore, they named this species Takenoshin Nakai swallow-wort (Vincetoxicum nakaianum K.Mochizuki & Ohi-Toma).

Vincetoxicum Wolf (Asclepiadeae) is the third largest genus in the Asclepiadoideae consisting of about 260 species geographically extending from tropical Africa, Asia and Oceania to temperate regions of Eurasia.

A total of 23 species are known from Japan, including 16 endemic species. Molecular phylogeny divides Japanese Vincetoxicum into four groups: the “Far Eastern” clade consisting of 11 endemic species and 4 more widespread species, 1 sister species to the “Far Eastern” clade, the “subtropical” clade consisting of 2 species and the “Vincetoxicum s. str.” clade consisting of 5 species.

V. magnificum (Nakai) Kitag. (Japanese: tachi-gashiwa) is closely related to V. macrophyllum Siebold. & Zucc. (Japanese: tsukushi-gashiwa) and V. macrophyllum var. nikoense Maxim. (≡Cynanchum nikoense (Maxim.) Makino; Japanese: tsuru-gashiwa) which belong to the basal lineage of the clade “Vincetoxicum s.str.”.

These three taxa have been recognized in several publications so far, including the current Japanese flora. Recently, the author introduced V. magnificum in Curtis’s Botanical Magazine, but the name is not legally published according to the International Code of Nomenclature.

The species was first published by Nakai (1937) as C. magnificum Nakai, in connection with a taxonomic study of the related species V. macrophyllum (as Cynanchum grandifolium Hemsl.) and V. macrophyllum var. nikoense (as Cynanchum nikoense (Maxim.) Makino).

In the publication, the name C. magnificum Nakai was proposed for the “tachi-gashiwa” population distributed in the Kanto region of Honshu, Japan, but no Latin description, diagnosis or even indirect reference to a previous description was given. Therefore, the name C. magnificum Nakai is a nomen nudum (ICN Art. 38.1 and 39.1).

Later, based on this nomen nudum, Kitagawa (1959) published V. magnificum (Nakai) Kitag.; therefore, this combination was not validly published. Furthermore, the name cannot be considered a novum species, “Vincetoxicum magnificum Kitag.”, because it is not accompanied by a description, diagnosis or reference to a previously published Latin description or diagnosis.

In the present study, the Japanese species “tachi-gashiwa” was validly described as V. nakaianum K.Mochizuki & Ohi-Toma with a detailed description. In this case, the proposed name is not “nomen novum” but “species nova” because C. magnificum and V. magnificum have never been legally published.

V. nakaianum is morphologically similar to V. macrophyllum but is distinguished by erect stems ending in inflorescences and larger flowers, green to brownish, 10-15 mm in diameter. (vs. dark purple flowers and 4-5 mm in diameter) with glabrous crowns (vs. villi).

Flowering March-May and fruiting June-February. Elevation 100-850 m. This species grows in Japanese cedar plantation forests and deciduous forests dominated by Fagus japonica Maxim., Abies firma Siebold & Zucc., Quercus L., Acer L., and Carpinus L. The species epithet is given in honor of Prof. Takenoshin Nakai (1882-1952).

Original research

Mochizuki K, Nemoto S, Murata J, Ohi-Toma T (2024). Vincetoxicum nakaianum (Asclepiadoideae, Apocynaceae), a new species from Japan for Cynanchum magnificum Nakai, nomen nudum. PhytoKeys 247: 191-201, DOI:10.3897/phytokeys.247.125070

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