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 mistaken 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.

Credit goes to Janet Wright for most if not all of these tips, as well as her generosity in sharing her knowledge with the community :)

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. rotundifolia, if at all.

(Note: update on angular vs terete stems)

Differentiation via length and shape of peduncle

Peduncle = the stem to the berry cluster

S. bona-nox has peduncles that are way longer than the leaf petioles, and are flattened like a belt.

S. rotundifolia has peduncles which are about equal or shorter than the surrounding leaf petioles, and not flattened:

Differentiation via number of seeds in berry

Smilax bona-nox will consistently have one big seed in each berry
Smilax rotundifolia will have 2-3 seeds per berry

Example observations:
S. bona-nox
S. rotundifolia

Set of observations with disagreements between these species:,60746&order_by=votes&place_id=1&verifiable=any


Posted on March 16, 2022 01:02 AM by arnanthescout arnanthescout


Nicely done!

Posted by janetwright 6 months ago

@janetwright hey, couldn't have done it without you :) thanks for sharing your knowledge with the community!
I should really start IDing these more, or at least spread word of this post to inform people about this species pair. Haven't been sharing it much since I'm not much of a advertising-type person, but it looks like many people have found it useful. Though I'm only familiar with the 3 species in Central Texas, I can curate what I can. I could probably learn all the species in Texas, though it'd take time to get confident with them.

Posted by arnanthescout 6 months ago

There's a BIG backlog of 'Needs ID" Smilax in Texas. I chip away at them from time to time, but they accumulate faster than I get to them. The vast majority are Smilax bona-nox, but there may be some others in there. That's a nice exercise in identification if you want to take some of it on!

In the field I often have to hunt around on a plant to find enough clues for a good ID, so a single iNaturalist photo may be inadequate, and we don't want to strain too hard to identify everything. Feel free to pass up ones that you're not sure about -- I certainly do. Thanks for this nicely illustrated guide.

Posted by janetwright 6 months ago

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