From away to garden.com and Robinhood Radio.com, this is Away to Garden with Margaret Roach. You're a weekly invitation to dig in and grow. In the age of climate change, my guest on today's reprise edition of the podcast told me, we can expect more poison ivy and meaner poison ivy. And I'd say from what I see growing around me and the rashes on friends that both are coming true. Though it may feel like it to many gardeners and others who spend time outdoors, poison ivy was not put on the planet to punish mankind for some sin or to boost antihistamine sales and dermatologic visits. As with every native plant, and yes, toxicodendron radicins is a native plant, and an important one at that, there's method to what seems like madness in the grand scheme of things. Poison IV is one of the plants I'm asked about regularly by listeners, so today we'll get a much closer look from a very safe distance in this archive conversation with Dr. Susan Pell and hopefully learn what we need to manage around it better, and also give it the respect it deserves. Dr. Pell is intimately familiar with Poison Ivy and its relatives because she has for years studied them right down to the molecular level. She's executive director at the historic United States Botanic Garden in Washington and also former director of science at Brooklyn Botanic Garden. On her LinkedIn profile alongside her impressive scientific credentials, she also says this that she loves to show people the coolness of plants. So keep an open mind gardeners as we explore the cool of poison ivy and of course practical more obvious matters like what to do to avoid that damn rash. So welcome Dr. Susan Pell. I want to talk about cool poison ivy. I absolutely do thanks so much and thanks for having me on the show. You're welcome. Well you're welcome. So first I think we should sort of just back up a little bit and tell people about the United States Botanic Garden where you are and also about your area of specialization, what you do your research in and so forth. Absolutely. So, the US Botanic Garden is located right at the foot of the US Capitol building on the mall in Washington, D.C. and we have a conservatory and some outdoor gardens here on the mall. And you can come visit exhibits here. We have public programs. We have a wonderful plant collection, diversity of habitats represented in our outdoor gardens and indoor conservatory as well. And actually there are some upcoming programs that we have that are going to tie into what we're going to be talking out about today. So we offer pretty frequently a medicinal and poisonous plants tour here at the garden. The next one is scheduled for July 7th, but it's offered pretty frequently. So that's a really fun one. Oh, interesting. Yeah, and then I'm actually going to be offering two programs myself. You can come and meet me here at the garden. And I'm going to be offering a tour of our roots exhibits that's happening

right now.

Did you say ROTS or R-U-H-R-H-U-S? It's R-O-O-T-S. So the name of the exhibit is exposed, secret life of roots. And that's happening until, it'll be up until October 13th, but I'm offering a tour of it on September 12th. And also be doing a presentation, a lecture on the routes that we find in our grocery stores

and association with that exhibit. Oh, okay, good. And so now your special area of concentration in your research over the years has been the cashew family, yes? That's right. Yeah, the cashew family. And I studied the evolution and the diversity of the cashew family, which includes poison

ivy among its members and pistachios and mangoes, sumac, smoke trees. A lot of wonderful plants that gardeners will be familiar with. So smoke trees cattinus is in there? That's right. Oh, interesting. You see, now that's why I did not, you know, that totally like fled from my mind, from whenever I used to maybe know it.

Interesting, so that's related as well.

It is, it's actually fairly closely related to poison ivy. Huh, okay. Now everyone don't be afraid of your smoke bush now. Or your sumac, right? That's the point in sumac. Ruth, the genus Ruth is absolutely fine. Yeah, okay, good. So the members of the cashew family that most, American gardeners are aware of, of course, are poison ivy and poison sumac. So what are their native range? Like how widespread are they? So poison ivy is found, kind of depending on how you recognize that species. There are some very closely related species, I'll call them sister species, to poison ivy. But if you include all of those under the umbrella of the common name poison ivy, and poison ivy is found in every United States except for the state of California. So, California will be the only state in which you don't find poison ivy. Although you do find poison oak there, so it gets its share of the Jesus toxicodiner in a that way. Okay now I said maybe I ironically said

sumac is poison sumac poison oak way to second now so tell me the genus and species of all of them. Yeah so let me just let it out right. Sorry. You did mention poison sumac as well. Okay. So the genus that we're talking about today this genus that causes a rash is toxicodinous. Yes. when toxic tree and poison ivy poison oak and poison sumac are all species within that

genus yes

so causes a rash is toxicodendron, when toxic tree. And poison ivy, poison oak, and poison sumac are all species within that genus. Yes. So common names are where we get into the trouble area. So in a very strict sense, poison ivy is toxicodendron radicans. Yes. And toxicodendron radicans is found from the Midwest to the Eastern United States. OK. But if other species like toxicodinrin ride burgi eye and some other species that are found within that genus, they all get called poison ivy, then expand the range to be almost the entire United States with the exception of California. So what beauty in this does California get? I'm sure they don't escape entirely, right? They've got something, have poison oak yes they have toxic and then diverse alone okay and it is quite nasty in fact i've seen some reports suggesting that fifteen percent of the state of california's entire workman's comp budget is spent on poison oak related absence of work and work and that's mostly due to firefighters uh... so people who are fire who are fighting those wildland fires that happen uh... they if they're in an area that has poison oak which a lot of California does have poison oak and they're in caling that smoke they can be in the hospital or certainly out of work for you know we can't time it is that's one of the things that one is always warned about is that if you do have debris from any of these plants, do not burn it. Yeah. That's absolutely correct, definitely. And then Poison's Sumac. What is its species then? Poison's Sumac is toxicodidrin vernic. It is found in pretty much just in the Eastern United States. range is a little bit more restricted than toxic and in rad cans is and so it occurs from

Texas found in front and pretty much just in the eastern united states oh it's range is a little bit more restricted and toxic and in rad can is and so it occurs from taxes in Louisiana on eastward but it really only gets it doesn't get deep into the midwest certainly doesn't get into the western United it's really more eastern slightly into the eastern part of the midwest and over to the coast so and it's in wet areas and very close to the city. Right, OK. So in two areas, I'm surrounded by a state park, the Teconic State Park, my garden is. And I have, so in two areas of the woodland edges of my garden, I lost trees or big parts of trees last fall. So the conditions sort of changed. And when the spring, when the snow melted and things started warm up and things started started to grow it was like poison ivy had just like romped in in about five minutes it was like it was poised for the opportunity or something is that it's typical behavior like what is its behavior isn't an opportunist like that it definitely is and so you know poison ivy is what I would call or what is called a successional plant, meaning that it really takes over in areas that have been either newly cleared by the building of a roadway or maybe they're continuously mowed or in your situation if you have a tree fall down. What happens there is that there's a new resource that's available on the ground level of that habitat and that's light. The light is being let in now. So Poisson IV is going to either deeds will germinate or the rhizomes, these underground horizontal stems that are, in many cases, underfoot where you don't even know they are, they may sprout stems. They come up above ground and you'll see them. There may have been Poisson IV there in a very light way before, maybe a few plants here and there, and then once that light resource is released by the, you know, the taking down or the falling of a tree, then that plant, those plants are able to really, you know, thicken and grow a lot more stems and really take over an area. So it's a six early, successful plant. It does very well-indisturbed areas. People, some people, would call it weedy. Yes, weedy. But, and we have some other thoughts about that. But first, you mentioned, so the rhizomes, one way it moves around just by rhizomes, and then it has fruits, so it can also be moved around by birds and maybe mammals, I don't know. That's absolutely correct. So, the fruits of poison ivy are actually an important food for wildlife. A lot of birds eat them. A deer have been known to eat them. Some cases rodents like mice eat them as well. And so they do get moved around through animals' guts and they deposit in various places away from the plant. And then they do have these underground horizontal senses, these rhizomes that are able to sprout and grow through the ground and create new plants there. So there was sort of a nursery rhyme wisdom I was taught decades ago from a book I had about Poison Ivy and it said, Leaves of Three Run and Flea. But really it's not so easily identified or typecast as always three leaflets and so forth. It can be quite variable, can't it? It absolutely can. So the leaves can be shiny or not shiny. They can have those red stems or red petals or not. They can be green sometimes. The shade of green is very different in the leaves. The leaves can be quite large. They can be one leaf that could be the size of your head or can be the size of one of your fingers you know they can be enormous or they can be really quite small and interestingly in some areas occasionally they will have five leaflets instead of three now that's very rare but in there is there is a population in Texas that apparently this characteristic has become fixed in this population so the entire population of poison ivy there in this one area actually has five leaflets and i have seen occasional collections from other states uh... that have that that characteristic as well but for the most part of the leaves of three runnethy or the leaves of three let it be there pretty good rinds are a member for the most part i would say okay but uh... they say everything grows bigger in texas so five instead of three that's right here you know three leaflets but um... and you know the edges uh... You the edges can be quite different. I mean, it is amazing. You really have to look carefully, because it's not always the same sort of visual image that you stored in your head the first time you saw it. It's so true. The margins that leave maybe smooth, or what we call entire, they maybe toost, sort of very jagged, or they may look like an oak leaf. Oh my and the habit of the plant that what I'm seeing like Russian to these two areas where I had disturbance or change in light conditions is one thing that's you know it's coming from the rhizomes and it's just herbaceous looking near... near the ground i mean it it looks like a ground cover right but it can of course go vertical and along my road there are many big sort of hairy looking what he vines wrapping around trunks of very old large trees so what what's that about so that's right i mean it can have a very you know quite different habits depending on where it's growing, what conditions it's under, and also depending on probably some of the genetic makeup of the plan as well. So some of these things that historically have been treated as separate species, or maybe as varieties, or subspecies of poison ivy, all of these things together. Sometimes there's one characteristic that's used to sort of recognize that, maybe that it's free standing instead of climbing but really if we look across poison ivy we see that it can be a climbing plant like you said sometimes those climbing plants can have quite large trunks of their own and big branches such that if they're growing on you know up a tree the the branches of the tree if you look closely may actually be poison ivy branches not the branches of the tree sometimes the is on as dead, and it looks like it's the tree. My goodness. Little shop of horrors. Absolutely. And sometimes they can be small kind of ground cover, like you're describing for small and free standing. And I've seen in coastal New Jersey, for example, I actually saw a shrub of poison ivy that was about seven feet tall, it had smooth black bark, and it

was definitely poison ivy.

I mean, it was very obviously poison ivy except that it was this really weird big shrub

with black Chinese bark.

Wow.

All right.

So, it's variable.

It is.

So, it's an important plant, ecologically, and I mentioned this in the introduction, and

actually, it's even a beautiful plant, excuse me, for instance, like in the fall and fall color. I mean, there's nothing quite like it. But nobody likes it except for you, because it causes an allergic reaction in some people. Now, I have to confess to everybody, I've been crawling around in the underbrush for most of my adult life, and I've never had the rash. I've never gotten quote, poison ivy. So I'm in some minority, I guess, of the population.

What about this list?

That's right. Yeah, so about 10% to 15% of the human population is immune to poison ivy and will never have a rash. Now, I have given lectures, you know, come around the country about this topic. And I frequently have, we'll have somebody come up to me It says, I'm in my 60s and I never had poison ivy and all of a sudden now I get the rash

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