There are observations of this species in iNat under two different names: Cynanchum barbigerum and Metastelma barbigerum. According to www.itis.gov, M. barbigerum is the accepted name. The Plant List also has M. barbigerum as accepted, while Cynanchum barbigerum is unresolved. BONAP still has Cynanchum barbigerum, however.

Since they are the same species, I'm going to merge them together into M. barbigerum. The name can be changed later if consensus is reached.