Cynanchum thesioides (Freyn) K. Schum. is one of the most widespread species of Cynanchum L., a large genus in the family Apocynaceae. It is found in temperate northeastern Asia, from eastern Kazakhstan, Mongolia, northern China to the Korean Peninsula. Its morphological characteristics are highly variable, adapting to a wide range of habitats.

During taxonomic studies on Cynanchum, researchers from the Wuhan Botanical Garden (WBG) of the Chinese Academy of Sciences (CAS) found that the distinctions between C. thesioides and C. gobicum Grubov are questionable. The latter is endemic to Mongolia and can be distinguished from C. thesioides by its long and fragrant stem, broader lanceolate leaves and puberulent (as opposed to glabrous in C. thesioides) outer surface of the corolla.

To address this issue, the researchers conducted field surveys, examined numerous plant images and specimens, and reviewed the relevant literature on the species.

Results showed a continuous variation in the morphological characteristics of the C. thesioides, including habit, leaf shape, leaf size, indumenta on the inner and outer surfaces of the corolla, and the relative lengths of the stigmatic head and corona, which encompass all the characteristics of C. gobicum. Thus, C. gobicum is in synonymous with C. thesioides.

Meanwhile, Vincetoxicum sibiricum f. linearifolium Debeaux is also newly synonymized, a name long neglected since Debeaux described it in 1877 from specimens collected in Shandong, China in 1877.

Finally, a thorough revision of this species is provided, including a new description, an updated distribution, and typification of all related names, including new lectotypification of V. sibiricum var. australe Maxim. and V. sibiricum f. linearifolium.

The study, entitled "A taxonomic revision of Cynanchum thesioides (Apocynaceae) with two new synonyms," was published in the PhytoKeys and funded by the Biological Resources Program of CAS.

Cynanchum thesioides growing in different habitats. (Image by WBG)

External morphological characteristics of Cynanchum thesioides. (Image by WBG)

Floral anatomy and fruit and seeds of Cynanchum thesioides. (Image by WBG)