1 INTRODUCTION
Cynanchum L. is one of the largest genera of Asclepiadeae
(Apocynaceae), and mainly distributed in Africa and Asia (Endress et
al., 2018). It has been considered as a ”dustbin genus” due to its
complex morphological characteristics, generally containing a
gynostegial, at least basally fused corona (Liede & Kunze, 1993). The
extent and classification of Cynanchum are controversial.
Markgraf (1972) and Ali et Khatoon (1982) supported thatCynanchum should be divided into Cynanchum ,Vincetoxicum Wolf, etc. But this taxonomic revision was not
supported by other scholars (Tsiang & Li 1977; Li et al, 1995). Woodson
(1941) and Liede (1997) suggested that more than twenty allied genera
were included in Cynanchum according to the characters of fused
corona etc. More than ten genera,which included RaphistemmaWall., are merged into Cynanchum based on abundant molecular and
morphological evidence recently
(Khanum et al., 2016). ButVincetoxicum was separated from Cynanchum with the
evidence of molecular, chemical and morphological characteristics (Qiu
et al., 1989; Liede, 1996; Liede, 2001; Rapini et al., 2007). Therefore,
the morphological diagnostic characters of Cynanchum were
expanded as: corolla 3–10 (–40) mm long; gynostegial corona highly
variable, usually with a ring of fused staminal and interstaminal parts,
staminal parts occasionally with adaxial appendage; occasionally with
additional free staminal lobe connate to ring (Endress et al., 2018).
In China, 57 species of Cynanchum were recorded in Flora of
China (Li et al., 1995). According to the recent revised
circumscription of Cynanchum and Vincetoxicum , 27 species
of Cynanchum have been transferred to Vincetoxicum , and
nine species of the allied genera have been included in Cynanchumwhich contain Adelostemma gracillimum (Wallich ex Wight) J. D.
Hooker, Graphistemma pictum (Champ. ex Bentham) Benth. et Hook.
f. ex Maxim., Holostemma ada-kodien Schultes, Metaplexis
hemsleyana Oliv., M. japonica (Thunb.) Makino, Raphistemma
hooperianum (Blume) Dec., R. pulchellum (Roxb.) Wall.,Sichuania alterniloba M. G. Gilbert & P. T. Li. (Khanum et
al., 2016), Sarcostemma acidum (Roxb.) Voigt (Liede & Kunze
2002; Liede & Täuber 2002). Recently, two new species ofCynanchum were reported from China (Shen et al., 2019; Xu et al.,
2021). There are 41 species of Cynanchum recorded in China by
now.
We collected an unknown species in
Ruili, Yunnan during field survey in
2020. This species has many typical characters of formerRaphistemma (included in Cynanchum ) with large and
reniform leaves, large and campanulate corolla. We are unable to match
it with any recorded species after the careful examination of the
specimens and literature from China and neighboring countries, and the
molecular phylogenetic results strongly support that it is an
independent species within Cynanchum also. Therefore, we describe
it here as new.