HEBERLING LAB

Watch out for poison ivy!  Both because it is a fascinatingly cool plant but also a potentially dangerous one. 

This flowering specimen of poison ivy was collected on May 31, 1903 by John Shafer (first curator of botany at Carnegie Museum) and O.P. Medsger in the Laurel Highlands of southwestern PA.
 
Poison ivy (Toxicodendron radicans) is a woody vine found in forest understories, but does especially well on forest edges. It is very common in urban and suburban environments. It takes many forms, climbing high up a tree, along the ground, or even a short shrubby thing. The leaves take a range of shapes, but as the adage goes (“leaves of 3, let it be”), it has three leaflets.
 
Poison ivy is known by many for its chemistry, producing a class of organic compounds call urushiol found in the plant’s sap and on leaves/stems/roots that cause a nasty rash to those who touch it. Not all people have a reaction (but most are sensitive), but don’t be too confident - it can develop with repeated exposure.  Incredibly itchy, the rash can become a serious health issue if infected, and especially if it oils get in contact with your eyes, face, or throat.  The rash can appear days after exposure and can last for weeks.
 
Research indicates poison ivy will get more poisonous with climate change, both in terms of growth and producing higher quantities of forms of urushiol particularly toxic to humans.
 
It is often considered a “weed” because of its fear-causing rash, but it is native to eastern North America.  The species has a wide distribution across our region, and across the world (native subspecies in China). Although native, the species seems to be getting more common as we create more forest edge habitat.   The colorful foliage can be quite beautiful in the fall, and the berries are a food source for birds and other animals. Humans seem to be the only ones allergic to it.
 
Poison ivy is often confused with other non-poisonous and poisonous plants. Some common confusions are 1) Virginia creeper (Parthenocissus quinquefolia), a vine in the grape but different leaves, and not with leaves of three and 2) Box elder maple (Acer negundo), a tree that has compound leaves unlike most stereotypical maples,  but with samaras (aka “helicopter” seeds).  
 
Poison ivy and some other rash-causing plants are in the cashew family (Anacardiaceae) – which also includes poison oak (not found in Pennsylvania, but in western USA), staghorn sumac (not rash causing), poison sumac (rash causing, but you likely won’t come across it unless in very wet habitats)....and even a few familiar species like  pistachio,  cashew, and mango (some people are allergic).  
 
What an amazing plant. 

This specimen image is now publicly available online: http://midatlanticherbaria.org/portal/collections/individual/index.php?occid=12232529&clid=0

In July 2017, I collected poison ivy, and was not careful.  Poison ivy rash on  your finger  tips is an awful experience.  This picture was from weeks after.

Don’t touch that! This leafless specimen of poison ivy (Toxicodendron radicans) was collected by C.H. Morgan on March 11, 1922 near Port Vue (near McKeesport just outside of Pittsburgh). Although best admired from a distance, poison ivy is a remarkable plant.  And like it  or not, a plant that has become a part of our urban landscape.  The leaves can be spectacularly red colored in the fall with beautiful berries. But still, do not touch. Not all of us are allergic to poison ivy, but even if you don’t think you are, you can become sensitive to it in time.  (From experience, getting the rash on your fingertips is not fun at all...)
 
All parts of this species are considered poisonous, containing the group of chemicals causing that nasty rash in humans, urushiol. Only humans are susceptible to the rash, as poison ivy is eaten by other animals. Getting it on your skin can be painful. The oils can also be inhaled (when burning wood) and cause serious respiratory illness or damage to eyes.
 
This particular specimen may not have leaves like most herbarium specimens, but check out the impressive aerial roots on the left. Poison ivy is a trailing or climbing vine (or even shrub) that can be quite diverse in terms of leaf shape and growth habit. In addition to its distinctive leaves of three, climbing plants have noticeable aerial roots, adhering the vine to the bark of host tree.
 
Why does poison ivy produce urushiol?  The answer is not totally clear, but probably not to deter humans, but instead as an antimicrobial agent.
 
Note the specimen label reads “Rhus toxicodendron.”  Although  the species is related to sumac (which are in the genus Rhus), poison ivy is now recognized in a separate genus, Toxicodendron, which means “poison tree.”
 
Poison ivy is native to North America. The species in the cashew plant family (Anacardiaceae), which includes several other species which produce skin irritants. In addition to poison ivy, poison oak, and poison sumac, the family also includes mango and cashew.  Interestingly, the shell of the cashew nut contains chemicals that can cause similar allergic skin reactions as poison ivy.
 
Research indicates that poison ivy may be doing better in a warming world, both in terms of growth and producing higher quantities of forms of urushiol particularly toxic to humans. Poison ivy also  tends to do well in disturbed environments, such as urban areas.
 
This specimen image (and all other poison ivy specimens in the region) are available online: http://midatlanticherbaria.org/portal/collections/individual/index.php?occid=12232543&clid=0

​Nancy Hanks Lincoln (mother of Abraham Lincoln) died on Oct. 5, 1818 from “milk sickness.”  Milk sickness is caused by poisoning after drinking milk from cows that have eaten the plant white snakeroot (Ageratina altissima).  Also known as “puking fever” or simply “the trembles,” early European-American settlers in the Midwest initially thought milk sickness was an infectious disease.  It was soon realized that the unidentified illnesses were caused by drinking milk from cows that ate white snakeroot, which contains the chemical tremetol, a toxin which causes weakness, pain, vomiting, abdominal pain, and can lead to coma and death.  The cattle of these early settlers often wandered into the forest to graze, seeking additional forage outside limited pastures.  However, milk sickness is very uncommon today due to modern farming practices and cows rarely have access to eat this plant.
 
White snakeroot is a fall blooming, shade-tolerant species found in forests across the Eastern US, and commonly found throughout southwestern PA.  This specimen pictured was collected in 1998 in southwestern Indiana, about 90 miles north of the Little Pigeon Creek Community, where Abraham Lincoln’s family lived.

Giant hogweed (Heracleum mantegazzianum) is considered a significant public human health concern.  This non-woody plant can be 8-20 feet tall with leaves up to 5 feet wide!  In fact, it took 6 separate herbarium sheets to capture the characteristics of this species.  This specimen was collected from a garden, where it was intentionally grown for the purposes of educating the public about this plant.  Native to central and southwest Asia, this plant can now be found in parts of Europe, Australia, New Zealand, and North America.  It is thought to be eradicated in Pennsylvania.
 
This plant is highly poisonous and designated as a federal noxious weed.  The sap of giant hogweed causes “phytophotodermatitis,” meaning serious skin inflammation occurs when contacted skin is exposed to sunlight.  Skin rashes can be very severe.  The sap is also said to cause blindness.
 
Giant hogweed, like poison hemlock and Queen Anne’s lace, is in the carrot family (Apiaceae).  It might be confused with the related native plant, cow parsnip (Heracleum lanatum), but giant hogweed is noticeably larger in height and flower size.

Collected on June 23, 1993, this specimen was found by Fred Utech near the Loyalhanna Creek in Salem Township, PA.
 
Don’t let the “weed” in common name affect your opinion of this plant!  Butterfly weed (Aclepias tuberosa) is a beautiful plant and the pollinators love the bright orange flowers.  Native to eastern North America, it can be found in dry, full sun conditions.  It is a great plant to add to your garden! 
 
Like other milkweeds (butterfly weed is in the milkweed genus), butterfly weed flower clusters mature into seed pods which eventual dry up to release airborne seeds in the late summer.  The long silk-like hairs (called pappi, or singular: pappus) have been used by native Americans to make textiles.
 
Despite its looks, butterfly weed is poisonous to ingest.  Like other milkweeds, this plant contains defensive chemicals called cardiac glycosides, which are poisonous to humans, livestock, and pets.  Milkweeds vary in their toxicity depending on species and age of plant.  Symptoms can include: weakness, difficulty breathing, kidney damage, cardiac distress, pupil dilation, loss of muscle control, and respiratory paralysis.

Butterfly weed flowers open early- to mid-summer (above).
Seeds burst from pods and blow in the wind in late summer (below).

Collected on June 16, 1925, this specimen was found near Shinglehouse, Potter County, PA by H.W. Graham.   
 
Poison ivy (Toxicodendron radicans) is a species you might be very familiar with!  Poison ivy is a native woody vine found in wooded areas, along paths, and edges of woods across the eastern United States.
the species can take various forms and habits, growing as a vine along the ground, up a tree, or as a small shrub. 
 
Poison ivy is famous for a chemical it produces, urushiol, which upon contact, can cause a severe skin rash in humans. The rash, which can last up to several weeks, can also lead to an infection due to intense scratching that breaks the skin. Serious health effects can stem from ingesting urushiol or can cause other allergic reactions in eyes and throat when inhaling smoke from burned plants.  If you come into contact with poison ivy, the best way to prevent an allergic reaction is washing with water and soap (or other detergent to wash off oils) as soon as possible.  Some people are more sensitive to poison ivy than others, or become more sensitive after repeated exposure.
 
Poison ivy is in the cashew plant family (Anacardiaceae), which includes several other species which produce skin irritants. In addition to poison ivy, poison oak, and poison sumac, the family also includes mango and cashew.  Interestingly, the shell of the cashew nut contains chemicals that can cause similar allergic skin reactions as poison ivy.
 
You might have heard “Leaves of three, let it be,” but what does that mean exactly? And how do you know if it is poison ivy, poison oak, or poison sumac?  Many plants might at first glance resemble poison ivy, but they can be easily distinguished.  Poison ivy is common in woods, forest edges, roadsides, and weedy areas throughout Pennsylvania, and has aerial, hairy-looking rootlets on stems of vines.  Poison sumac (Toxicodendron vernix) is also native to Pennsylvania, but is less common and only found in swamps and other persistently wet habitats.  Poison sumac (Toxicodendron vernix) has leaves made up of many more leaflets than poison ivy.  Lastly, poison oak (Toxicodendron diversilobum) is sometimes confused with poison ivy, but it is unlikely you encountered this species in Pennsylvania --  it is only native to the western United States.

Left: Poison ivy (Toxicodendron radicans), common in woods, trails, and forest edges in PA
Middle: Poison oak (Toxicodendron diversilobum), you might be out West
Right: Poison sumac (Toxicodendron vernix), you might be in a swamp

Collected on June 9, 1959, this specimen was in the woods along a road to Pocahontas, near Salisbury in Somerset County, PA by Leroy Henry.  Henry was the Curator of Botany at the museum.
 
Mountain laurel (Kalmia latifolia) is the state flower of Pennsylvania!  It is a broadleaved evergreen shrub native across the eastern US, especially in forests of mountainous areas.  This specimen was collected not too far from the highest point in Pennsylvania and the Maryland border.  Often mistaken for Rhododendron, both the Rhododenrons and mountain laurel are found in similar habitats and belong to the heath family (Ericaceae).
 
Despite its beauty, mountain laurel has a dark side: all parts contain toxins that are poisonous to humans, pets, horses, and cattle.  Ingesting this plant can cause vomiting, diarrhea, impaired vision, convulsion, cardiovascular distress and death.  Honey made by bees from mountain laurel can also cause medical problems to humans.  Benjamin Smith Barton (American botanist in late 1700s) wrote that “in the autumn and winter of the year 1790, many people died in Pennsylvania from the effects of wild honey, collected from Kalmia plants.”