Smilax bona-nox vs Smilax rotundifolia

This is a quick post to remind me of how to distinguish these two Smilax species. Smilax bona-nox is an incredibly variable species and sometimes it can be mistakedn for S. rotundifolia. With Smilax rotundifolia, it's less of a case of finding characteristics to look for, but more of looking for characteristics that would rule it out.

Differentiation via thorns on leaf nodes

Smilax bona-nox will have thorns at leaf/tendril nodes (Smilax glauca will also exhibit this characteristic). Smilax rotundifolia will not. If there are thorns at the leaf nodes, then it's NOT Smilax rotundifolia.

Differentiation via leaf margins

Smilax bona-nox has prickles along the leaf margins, which I suppose is where it got its common name "Saw Greenbrier." On some specimens this can be quite obvious, while on others they exhibit no prickles at all. However, prickles on the leaf margin will rule out S. rotundifolia. It is good practice to check multiple leaves for any prickles.

Both of these have prickles on the margins, but on one it's more obvious than the other.

Smilax rotundifolia often has a "minute roughness" on the leaf margin. This is one of the best characteristics to look for... though it can be hard to see or photograph. Not every S. rotundifolia plant will exhibit this, but it is pretty consistent. Besides prickles, S. bona-nox margins will be completely smooth to the touch, and can also have a "cartilaginous edge" - a cream colored border.

Minute roughness - though this is S. tamnoides, not S. rotundifolia

Note: S. tamnoides, the bristly greenbrier, also exhibits this minute roughness, so always check to see if you can find the needle thin, black prickles so you don't mix those up too.

Differentiation via leaf petiole color

Smilax rotundifolia tends to have pinkish coloration on its petioles, while Smilax bona-nox will have green petioles. If a specimen exibits a pinkish color on the leaf petioles, that is a good reason to lean towards S. rotundifolia

Differentiation via leaf shape, texture, etc.

I do not think these characteristics are as reliable as the other ones, but will list them anyways.
Smilax bona-nox leaves can have a three-lobed appearance. This can be more or less prominent on specimens, but if the plant is distinctly three-lobed that rules out S. rotundifolia.
Smilax bona-nox will also have "tougher, leatherier leaves," while Smilax rotundifolia has a brighter shine to it. Young leaves of both species tend to look shiny though so this probably applies better with mature leaves.
Smilax bona-nox often have light splotches on its leaves. Seldom will you find this on S. rotundiflolia, if at all.

(Note: update on angular vs terete stems)