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A Glimpse of Nature - Poison Ivy

If you are familiar with poison ivy, you probably think of it when it is green and leafy as in this photo from Queset Garden:


Young Poison Ivy Plant, June 25, 2020


This is to be expected since we humans spend more time outside in warm weather, when long days and summer vacations provide greater opportunities for outdoor work and play. Our perspective is, of course, a reflection of human self interest:  we pay more attention to poison ivy when it is most likely to affect us. The plant is out there year round.

You can see it in spring when its young leaves are shiny with a bronze tint.


Dense Poison Ivy Thicket, Hanson, MA, May 16, 2021


In summer its luxuriant green foliage drapes forest edges...


Marshfield,MA, September 6, 2020


...and in autumn the plant dazzles with a blaze of red.


Foliage on October 23, 2020 in Fairfax County, Virginia

Famartin, CC BY-SA 4.0


By Thanksgiving, its leaves have fallen and its gray-white fruit is conspicuous.


Poison Ivy Fruit Along Queset House Driveway, November 24, 2021


It is truly a plant with all-season interest!  Before we focus on the current season, let’s review a bit of this species’ natural history. 

Poison ivy is a very variable plant – seasonably, as can be seen in the above images – but also in its form, height, leaf size, and habitat preferences.  This is one reason, I believe, that people have trouble recognizing it.  Knowing one of these forms leads to overconfidence, that is, to the assumption that all poison ivy plants look alike.


In reality, this species can be a shrub or a woody vine.  It can form a groundcover only inches high...


Stems in Winter (less than 1 foot high), January 12, 2020


...or climb to the forest canopy on thick “trunks.”


Poison Ivy Vine with Aerial Rootlets, January 12, 2022


The vine climbs by forming aerial roots where its stem touches the tree.  A National Park Service article aptly calls them “fuzzy ropes.” They can reach remarkable heights.  Two studies cited by the U.S. Forest Service reported that “the main stem may be >160 feet long.”  In their effort to reach more sunlight, such vines can overwhelm the tree that supports them.


Moreover, poison ivy can grow under a wide range of conditions:  in sun or part shade, in different soil types, at various elevations, and in wet or dry situations.  It thrives along rivers and in floodplains, but it will also grow on coastal dunes and in meadows.  It is a pioneer species that prefers areas that have experienced “disturbance” such as lumbering or storm damage.  Look for it on forest edges and in gaps in the tree canopy.  This is a very common plant. It is little exaggeration to say that I see it on every walk in Southeastern Massachusetts.


Each day when I arrive for work at the Ames Free Library, I pass a significant patch of poison ivy along the Queset driveway.  Some grow on the ground along the road’s edge, but the more impressive plants climb trees next to our neighbor’s small pond.  Although I often take it for granted, this poison ivy “thicket” drew my attention on Saturday with the sound of birds flitting between its branches.


House Finch in Poison Ivy Tangle, January 8, 2022


The twigs in the above image belong to poison ivy vines, not to the supporting tree.  In the midst of this is a house finch who seeks a meal.  Yes, poison ivy is a valuable food for wildlife.  Dozens of bird species eat its fruit including woodpeckers and ground-nesting birds such as wild turkeys.  In fact, the plant's seeds are dispersed through bird droppings.  Mammals also consume the leaves, stems and fruit of this plant . . . and they and the birds do so unscathed.  Other than humans, only “primates and hamsters are known to have allergic reactions to Poison Ivy” according to Illinois Wildflowers, though I’d rather not know how they determined this.


Interestingly, poison ivy fruit is not highly nutritious.  The National Park Service calls it “low quality fruit” because it has a low lipid content, that is, it is low in fats, oils, and similar substances.  While it may not be a favorite meal, poison ivy provides a food source after more desirable options have been depleted.  Unlike some tastier berries, poison ivy’s drupes are still available in winter.  When I compare photos from Thanksgiving and this week, it’s clear that birds have started tapping into this source.

This short video clip shows two finches actively feeding.  They certainly don’t share our perspective on poison ivy!



Note:  Like most people, I develop a rash when I’m exposed to poison ivy’s oil, urushiol.  The experience is never pleasant.  In most cases, the rash has been mild, though on one occasion I acted foolishly.  I was gardening, in a hurry, and without protective clothing. In the process of digging up transplants, I also chopped poison ivy rhizomes into bits. This led to a visit at the walk-in clinic.  Don’t underestimate the plant, but don’t panic either.  A few common sense behaviors can lessen your risk of exposure.

–Learn to recognize the plant’s varied forms.

–Bring appropriate clothing for the location.  Long sleeves and long pants are sometimes necessary, but you don’t usually need a suit of armor.

–Wash yourself and your outer clothing as soon after contact as possible.


Read Smithsonian’s“A Poison Ivy Primer” for good information about the plant’s effects on people, especially the way that urushiol tricks the human immune system.


With familiarity, poison ivy simply becomes part of the landscape:  give it space, respect its value as cover and food for wildlife, and enjoy its beauty . . . even in summertime.


Growing Along The Guardrail At Robinson’s Creek, Pembroke, MA, August 19, 2020

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