In the past it was often a genus of its own under the name Nemexia and taxonomists still need further study of the species of Smilax to determine its proper rank.

[1][2] However the widely accepted taxonomic system of the Flora of North America does not recognize Nemexia, nor does the AP-site.

It is hypothesized that the ancestor of this section evolved in Asia and spread to North America via the Bering Strait land bridge.

But according to the abstract of reference 2 (Fu et al. 2005) "Results strongly support a clade of two well-defined East Asian species, Smilax riparia and S.

Thus, the entry should read: "The two East Asian species, S. riparia and S. nipponica, formed a clade."