eastern poison ivy (Toxicodenron radicans)
eastern poison ivy
Rhus radicans L.
Rhus toxicodendron L.
Rhus toxicodendron var. malacotrichocarpa (A. H. Moore) Fern.
CONFIRMATION STATUS: Confirmed.
TAXONOMY: The currently accepted name of poison-ivy is
Toxicodendron radicans (L.) Kuntze. Poison-ivy is a highly variable
taxon. There is disagreement in the literature regarding this species
and its infrataxa. Recognized subspecies are geographical segregates.
Two subspecies present in eastern Asia are Toxicodendron radicans
ssp. orientale and Toxicodendron radicans ssp. hispidum. Subspecies
found in North and Central Americas are: 1) Toxicodendron radicans
ssp. radicans (Atlantic Coast), 2) Toxicodendron radicans ssp. barkleyi
Gillis (Mexico & Central America), 3) Toxicodendron radicans ssp.
divaricatum (Greene) F. A. Barkl. (Mexico & Arizona), 4) Toxicodendron
radicans ssp. eximium (Greene) Gillis (Mexico & Texas), 5) Toxicoden-
dron radicans ssp. negundo (Greene) Gillis (west of Appalachian Moun-
tains), 6) Toxicodendron radicans ssp. pubens (Engelm. ex S. Wats.)
Gillis (southeastern United States), and 7) Toxicodendron radicans ssp. verrucosum (Scheele) Gillis (Oklahoma & Texas). The Atlas of Virginia
Flora lists Toxicodendron radicans ssp. radicans as the only subspecies
occurring in Facquier County.
NATIVE STATUS: Native, United States and Canada.
GENERAL BOTANICAL CHARACTERISTICS: Poison-ivy is a
native dioecious shrub, subshrub, or woody vine with various growth
forms: dwarf, erect, decumbent, or high climbing. It grows from 1.6 to
6.6 feet (0.5 to 2 m) high. The trunk can grow to 5.9 inches (15 cm) in
diameter. Adventitious roots allow poison-ivy vines to grow to 150 feet
(45.7 m) in length. Rhizomes may be at the surface or deep in the soil.
Leaves are three-foliate and deciduous. Flowers are in axillary panicles.
The fruit is a dry, round drupe.
REGENERATION PROCESS: Poison-ivy reproduces vegetatively
and sexually. It sprouts from aboveground vines, rhizomes, and root
crowns. Plants take 3 years from seed to reach the flowering stage. Seeds
have an oily covering and are primarily dispersed by animals. Since the
covering is buoyant, the fruit is also dispersed by waterways. Poison-ivy
seeds that had passed through sharp-tailed grouse digestive tracts gave
good to excellent germination after both warm and cold stratification.
Seeds regurgitated by a crow exhibited 90 percent germination.
SITE CHARACTERISTICS: Poison-ivy occurs on a large variety of
sites. It is found in riparian communities, gallery forests, open dry or wet
woods, and hillsides. It occurs on sand dunes of lake shores and barrier
islands. Poison-ivy roots on the bases of cypress (Taxodium distichum) in
large peat mats. It is also found on hammocks. Poison-ivy is common in
disturbed places, such as roadside thickets, stone walls, fences, railroads,
clearcuts, and orchards. It also occurs in urban settings.
Poison-ivy grows in semiarid to humid regions. One exception is mari-
time areas where it grows in a perhumid climate with localized fog.
Climate is typically continental, with short, warm to hot summers and
long, cold to cool winters. Average growing season ranges from about
150 days at its northern limit in Quebec to 240 days in the south in
Poison-ivy occurs in a large variety of soil conditions. Soil textures may
be poorly drained clays with gleying and mottling present. Soils also may
be well-drained silty loams to loamy sands.
Topography is flatland to rolling hills. Poison-ivy also occurs on steeper
slopes in the southwestern states. Upper elevation limits for poison-ivy
growth are 7,080 feet (2,158 m) in New Mexico and 1,700 feet (518 m)
Poison-ivy is found under all moisture conditions; however, poison-ivy
occurs most frequently on moist, open sites.
SUCCESSIONAL STATUS: Poison-ivy is a common intruder into
ruderal sites in North America, while in Japan, it is a component of old
growth. Poison-ivy is an early competitor with other species that may
become established in the overstory. Poison-ivy is a primary dune
colonizer, establishing before the xerophytic evergreen flora. Poison-
ivy is somewhat shade tolerant. In general, the presence or absence of
canopy cover does not significantly influence poison-ivy growth.
Poison-ivy occurs in late seral and climax communities. In secondary suc-
cession of old fields, poison-ivy was present in seral stages of 30- to 100-
year-old stands (the pine stage with loblolly and shortleaf pines [Pinus
echinata]) and in 150-year-old stands (the pine-hardwood stage with
shortleaf pine, northern red oak [Quercus rubra], magnolia [Magnolia
grandiflora], and American beech [Fagus grandifolia]). In another study,
poison-ivy occurred in late seral stages of pine-hardwoods and in climax
communities of magnolia and American beech. Poison-ivy was present in
climax white oak (Quercus alba)- American beech communities.
SEASONAL DEVELOPMENT: Poison-ivy flowers when the leaves are
about half open. It blooms May to July throughout its range. Fruits mature
from August through November. Fruit may persist until the flowering next
season. Leaves are dropped after freezing temperatures in the fall.
GENERAL DISTRIBUTION: The range of poison-ivy extends from
southern Ontario east to Nova Scotia and Prince Edward Island. Poison-
ivy occurs in all states east of the southern Cascades, Great Basin, and
Mojave Desert. Populations continue southward through Central America
to Guatemala. Poison-ivy is also native to eastern Asia.
SKY MEADOWS DISTRIBUTION:
Vine specimens can be found on trails marked in red.
Appalachian Trail/Old Trail
South Ridge/North Ridge
Rolling Meadows/ Lost Mountain
HABITAT TYPES AND PLANT COMMUNITIES: Poison-ivy is not
an indicator or uniquely associated with a particular community type. It is
a dominant understory plant in Gambel oak (Quercus gambelii) community
type. Poison-ivy was one of the seven most frequently occurring plants in
the herbaceous layer of a shagbark hickory (Carya ovata) community type.
There were an average of 3,540 stems per acre (8741 stems/ha), with 80
individuals attaining a size class 2 (0.01-0.5 inch [0.03-1.3 cm] d.b.h.).
Poison-ivy was an understory dominant in a northern pin oak (Quercus
ellipsoidalis)- cherrybark oak (Quercus falcata var. pagodaefolia) com-
munity. Poison-ivy occurred with 55 percent relative frequency in the
Wisconsin habitat type white pine/hog peanut (Pinus strobus/Amphicarpa
Common overstory associates of poison-ivy are bur oak-aspen (Populus
tremuloides), green ash, American elm, Florida torrey (Torreya taxifolia),
southern red oak (Quercus falcata), and blackgum (Nyssa sylvatica). Add-
itionally, poison-ivy occurs with sycamore (Platanus wrightii), boxelder
(Acer negundo), wax myrtle (Myrica cerifera), and redbay (Persea
Common understory shrub associates are skunkbush (Rhus trilobata),
snowberry (Symphoricarpos occidentalis), common chokecherry (Prunus
virginiana), blackberries (Rubus spp.), trumpetcreeper (Campsis radicans),
and sweet fern (Comptonia peregrina).
Associated vines are greenbrier (Smilax spp.), grapes (Vitis spp.), and
Virginia creeper (Parthenocissus quinquefolia). Other species found with
poison-ivy are broomsedge bluestem (Andropogon virginicus), heartleaf
foamflower (Tiarella cordifolia), sweet spire (Itea virginiana), bracken-
fern (Pteridium aquilinum), and lizardtail (Saururus cernuus).
IMPORTANCE AND USES: Animals generally are not susceptible to
poison-ivy-induced dermatitis. In southern Indiana, poison-ivy was one of
the seven most important taxa consumed in winter by white-tailed deer.
Two studies showed that white-tailed deer preferred to eat poison-ivy over
other available browse. Poison-ivy leaves were eaten by white-tailed deer
with greater frequency in summer (81 percent) than in spring (67 percent).
Researchers have reported that white-tailed deer ate poison-ivy fruits as a
principal food item; fruits were consumed fall through spring.
Poison-ivy produces soft mast. A wide variety of migrant and resident
non-game and upland game birds consume the fruits; it is considered a
preferred species. Ripe fruits become conspicuous and are usually one
of the most abundant foods available for birds in fall and winter.
Poison-ivy is an important component in wetlands used for sewage man-
agement. Secondarily treated waste water or waste water from a septic
tank has been dumped into pond cypress (Taxodium distichum var.
nutans) stands for over 45 years; numbers of poison-ivy plants did not
decline. Researchers have compared vegetation occurring on cypress
domes after various treatments with waste water; poison-ivy persisted
despite the treatments. Nutrient changes did not exclude poison-ivy in
New Jersey wetlands; poison-ivy occurred with high cover in control and
developed sites near unpaved roads, septic systems along wetland edges,
and direct stormwater sewer outfall.
For 50 years, poison-ivy has been planted to prevent dike erosion in the
To restore Louisiana bottomland that had been cleared for farming, oaks
(Quercus spp.) were planted. Other species, including poison-ivy, were
allowed to move in naturally. Within several years, poison-ivy occurred in
all land sites in varying densities.
Poison-ivy sap has been used to make indelible ink.
Poison-ivy sap causes allergic contact dermatitis in humans. The active
agent is urushiol, which exudes from broken resin ducts in most plant
parts. Plants are variously poisonous depending on time of year and plant
maturity, and people vary in susceptibility. Symptoms and treatment are
detailed. Ingested leaves do not confer immunity and can cause humans
serious gastric disturbance.
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