Poison Ivy - "It'll Make You Itch !!"
A few days ago a neighbor asked me if the vine with leaves in groups of five that was
growing against her shed was poison oak. She had been assured by another that it was
definitely poison oak. I must confess that when I was six or seven years old, I was told
exactly the same misconception; leaves of three, poison ivy, leaves of five, poison oak.
So my brothers and I went around the neighborhood spreading false information.
Shortly thereafter another elderly neighbor got me straightened out proving that the
vine in question was, in fact, Virginia Creeper (Parthenocissus quinquefolia).
At times a somewhat invasive native of the United States much transplanted and loved in Europe for its graceful appearance and its brilliant scarlet fall foliage.
The real “poisons” that I will discuss here, are all members of the Cashew Family, genera Rhus and Toxicodendron. There are six that you may encounter here in Delaware; three are harmless (with red upright fruit clusters) and three that are poisonous to touch (with white drooping fruit clusters). I’ll start with the harmless ones and end with the “baddest” of the bad. The most commonly seen is the winged sumac (Rhus copallina), present in nearly every farm fencerow, meadow, or abandoned field, spreading by seeds and underground suckers to become large colonies.
Botanists can’t seem to settle on a single common name. Dwarf, shining, and winged sumac all refer to the same plant. The term winged refers to the little leafy projection running along the rachis (leaf stem) between the leaflets. The leaves of all the harmless sumacs are pinnately compound (like a feather), having a central rachis bordered by 7 to 31 leaflets in two parallel rows along the edges and one central leaflet at the tip. (See photos).
The second less commonly seen sumac in our immediate area is the smooth sumac
(Rhus glabra). The leaflets are medium green above, whitened beneath, lance-shaped
and saw-toothed margins.
Generally this is a larger shrub or small tree than the
previous species. There are several colonies on the Milford Millponds Nature Preserve,
on the Lee property and at Blair’s pond woods. All parts of the twigs, the rachis, and
leaflets are smooth. The bright red upright fruiting clusters are seen later in the summer
and fall. They make lovely additions to a dried flower arrangement.
The last of the harmless sumacs is the hairy or staghorn sumac (Rhus typhina). I have
not seen it on Nature Preserve lands but it is commonly seen farther north in Kent and
New Castle Counties as a small roadside tree or in abandoned fields. Once again the
seed heads are large, red and upright. In this case the twigs are thick reddish brown and densely covered with light brown hairs.
The petiole and rachis are hairy as well. After leaf drop in autumn, the bare branches resemble a stag’s antlers in velvet, hence one of the common names. There are several cut-leaved varieties that are sold as ornamentals. Formerly, there was one growing near Houston, Delaware on Rod and Gun Club Road but it has now disappeared.
The foliage turns brilliant colors in the fall but the habit of sending up suckers makes it undesirable as a lawn tree.
Poison Ivy, (Toxicodendron radicans), seemingly grows everywhere in all types of habitats. In full sun or dense shade, in dry soil or in wet swampland. The leaves are trifoliate. (Clover leaves are trifoliate).
The leaves are shiny when young but at other times less so. Sometimes the leaf margins are entire (lacking any teeth) and at other times are coarsely toothed. The growth habits can vary from totally prostrate among meadow grasses, to upright brushy patches at the edges of woodlands, or climbing up trees, shrubs, or power poles by means of aerial roots to a height of fifty or more feet. The trunks of these vines can be as large as a man’s arm. All parts of the plant are poisonous to touch containing an irritating oil called urushiol. The worst case of poison ivy dermatitis that I ever endured was from digging in soil infested with their roots in January. So beware! You can spot poison ivy on all of the tracts of the Nature Preserve. Learn to identify and avoid it, “leaves of three, let it be” if you are sensitive. The fruits are grayish white in loose clusters but not always present.
In sharp contrast to poison ivy growing universally everywhere, I had never knowingly seen true poison oak, (Toxicodendron pubescens), that I could positively identify.
I had to enlist the help of our State Botanist, Wm. McAvoy, who gave me a precise location so I could get some photos to share. The location was 26 miles from Abbott’s Mill Nature Center. The habitat was a dry, gravelly roadside through a forested area in bright sun.
Poison oak plants grow unbranched, upright, between two and three feet high, with a few trifoliate leaves at the tip. To my eyes they appear more olive green, slightly more pleated, with coarser teeth on the edges than the leaves of poison ivy. The leaf veins and petioles, especially on the undersides, are velvety pubescent (a good field mark). The undersides of poison ivy leaves are smooth. Be sure to use a twig or other instrument to turn over and examine a leaf since all parts of poison oak,
like poison ivy, are poisonous to touch. The plants spread by underground stems and never climb. The fruits are a yellowish white in small clusters but are not always present. The plant is uncommon in Delaware and is S-3 in the Vascular Plants of Concern list. I have no accurate information about the severity of poison oak rash. Any volunteers?
Editor's note: I grew up climbing all over the poison oak infested hills of southern Oregon and the only poison ivy we were aware of was in "The Coasters" well known 1959 song. I have always thought that the song gave poison ivy a bad rap, as poison oak was a much worse problem for us there than poison ivy is here. However, I have just learned that western poison oak is entirely different from the poison oak found in Delaware. My advice is: Don't trust any of it, and if you travel out west, be especially careful. Steve C.
Lastly is the most virulent of them all, poison sumac, (Toxicodendron vernix). Luckily for us trekkers, it grows chiefly in wet forested swamps where the hiker is not apt to go. It too, is uncommon and listed as S-3.
Over the years I have located four plants on the Abbott’s Mill property. The largest of those, a small tree near an observation platform, I formerly used while teaching classes. That particular tree has since died and a new, younger tree has been located. One tree on the Mill Property is large enough to stand under. (See photo). Growth habits range from a large shrub to a small tree. The leaves are pinnately compound, however the rachis is smooth (and reddish in the specimens I have seen) and the leaf edges are always smooth without any teeth (termed entire).
The twigs have small raised dots called lenticels and are arranged on the stem alternately. This is very helpful for distinguishing poison sumac from ash trees that share the same habitat, since the ash twigs and branches are arranged directly oppositely. (See photo). Once again the fruits of poison sumac, if present, are white and hang in loose clusters.
All three of these plants contain the irritating oil urushiol that causes severe dermatitis in sensitive individuals. If you suspect you have been exposed and you are allergic, wash the infected area as quickly as possible with strong soap and water. Be sure to completely rinse the oil from your skin. Do not use a beauty bar or other soaps containing lotions which simply mix with the irritating oil and spread it farther. Personally, I recommend getting the proprietary soaps that are now available from the drug store. The new products are very effective and your best choice. Also keep in mind that your gloves and other clothing, even you pet’s fur can easily carry the persistent oil. The oil is not volatile so you cannot get poison from walking too close to these plants. The one exception that I know of is from smoke. Smoke from burning these plants can carry for some distance and cause severe dermatitis. This has been a problem for firefighters fighting brush fires.
Editor's note: For more about poisonous plants see this recent warning from the Delaware Department of Agriculture:
So learn to recognize and avoid these plants then get outside and enjoy your Milford Millponds Nature Preserve. First time? Start by slowly walking the boardwalk loop beginning behind Abbott's Mill.
It is a short, easy, beautiful walk with plenty of resting benches and lots of shade and it is A.D.A. accessible. A plant identity guide is available for your cell phone or other device.
Special thanks to: Wm. A. McAvoy, Delaware Natural Heritage Program