How do you tell the difference between poison ivy and kudzu?

September 7, 2014 9:00 AM

So, I'm vacationing in the Cherokee National Forest in Tennessee, and my plant identification skills are useless around all this kudzu, apparently. I know poison ivy has a few distinguishing characteristics, but they all seem to overlap with this annoyingly omnipresent vine.

So far, kudzu and poison ivy seem to share some similar characteristics:

• Leaflets that come in three (trifoliate), with the top leaflet having a much longer stem
• Leaflet veins are alternate
• Leaf stem curls around the base stem instead of just forking off -- does kudzu do this?
• Leaf placement is alternate and not parallel

I know there are some differences in leaflet shape -- kudzu is a little more lobe-shaped and less pointy than poison ivy, but there seems to be a lot of variation in both species. Aside from that, the only place left to look is the flowers and seeds, which aren't always present. Extracting resin seems to be a little to risky -- I'm unbothered by the urushiol, but some of my friends have drastic reactions. Are there any other ways to tell these two apart?

posted by ayerarcturus to Science & Nature (6 answers total)

Poison ivy isn't a vine, first off. Poison ivy tends to be sort of "underbrush" type ground cover. (Though sometimes it can grow up onto trees, ack!)

It might be easiest to think of kudzu as "horizontal" and poison ivy as "vertical". If you see shoots growing vertically up in the air from the ground, that's more likely poison ivy as opposed to kudzu. Kudzu is going to vine outwards in all directions, not send shoots up towards the sky. Poison ivy is the kind of plant that will turn into a bush if it's allowed to get out of control. (In fact, if it looks like kudzu in bush form, it might well be poison ivy.)

Poison ivy is really common in areas that are commonly mowed/cleared, but haven't been recently. You're going to see it along paths and in clearings, and possibly at badly maintained campsites. Which is where I'd be most worried about encountering it in terms of getting a rash from it.

But, honestly, unless you're a horticulturalist or something, your best bet is just to steer clear of anything leafy and green that grows about shin level. Wear long pants, socks, and good shoes, and don't sit down in the underbrush.

In a strict plant-identification sense, to me poison ivy leaves look pointier than kudzu leaves, but for practical purposes, looking at what type of plant it is and where it is might be easier than comparing leaf shapes.
posted by Sara C. at 9:14 AM on September 7, 2014

Pretty sure poison ivy does grow as a vine in this part of the country, FWIW, although it can also be a shrub. Kudzu looks enough like it that you're probably better off just avoiding any suspicious three-leafed thing.
posted by dilettante at 9:34 AM on September 7, 2014 [6 favorites]

Best answer: I think the roundness vs pointyness of the lobes is the best thing to go by. Individual leaves may have some variation, but you're rarely looking at a single leaf. If the overall leaf pattern is mostly round, lobed leaves it's kudzu, and if most of the leaves have pointy lobes it's poison ivy. Also kudzu leaves are larger than poison ivy leaves, and the undersides are hairy. Kudzu vines send out tendrils that wrap in coils, like bean plants. Indeed, the whole attitude of kudzu is like a bean on steroids, which makes sense because they are in the same family.

Here's a picture showing poison ivy and kudzu growing together. I don't think it's actually that difficult to tell which is which.
posted by drlith at 9:42 AM on September 7, 2014 [7 favorites]

Poison ivy also tends to be shiny and reddish in the fall and spring. It definitely can be a vine, though.
posted by geegollygosh at 9:48 AM on September 7, 2014 [1 favorite]

Best answer: Poison ivy will vine up a tree, but it usually won't have very many leaves up high. The vines are furry. If Kudzu is vining up a tree, the tree will probably be covered with kudzu.

One identifier for poison ivy is a small red dot, right where the three leaves come together on the stem.

Kudzu and poison ivy look pretty different to me. Kudzu is going to be a much denser plant, and is going to grow in thicker mats and climb higher. I have seen poison ivy as tall as 3 feet but never higher (unless its climbing a tree and then it will just be a few leaves here and there along the vine) and it doesn't grow in dense mats like kudzu, although it might form a line along the treeline.

Anyway, I can't imagine any reason why you'd be climbing into a mass of kudzu, so the general advice about avoiding plants with three leaves is probably best.

If you're interested in plant identification while you're out, try to find some jewel weed, which often grows near poison ivy and can be used as a remedy for it.
posted by natteringnabob at 10:53 AM on September 7, 2014 [1 favorite]

Best answer: Poison ivy often has notched leaves with a distinct pattern: the center leaf is notched symmetrically and the other two have larger notches on the outer edges.
posted by Johnny Wallflower at 4:56 PM on September 7, 2014 [2 favorites]