Not-so-Nice Native Plants

Planting native plants is one of the best ways to support our native pollinators, birds, and mammals, but some of these native plants have poisonous properties. You may find them growing as weeds in your yard or garden or in a meadow or wooded area when walking or hiking. As a means of defense, plants develop toxic compounds and some of these compounds are poisonous to humans. While these plants may be poisonous to humans, many are a valuable food source for our native pollinators, birds, and in some cases mammals. Many are larval host plants for a number of butterflies, their flowers attract a variety of bees, flies, wasps, moths, and butterflies, and their berries are eaten by birds and small mammals. Being aware of their poisonous properties can allow you to make a decision whether to eradicate them or allow them to remain for their ecological value.

Poisonous plants may cause skin irritation due to contact, physical symptoms due to ingestion, or both. They range in toxicity, and some may cause only mild toxicity, such as stomach upset or slight irritation of the skin, while others may cause more severe physical symptoms and even death. Besides the plant itself, other factors influence its toxicity and how severe the poisoning symptoms may be, such as the age, weight, and health of the individual and the quantity of the plant ingested. The part of the plant ingested, such as roots, leaves, and berries, and the form of the plant at the time of ingestion, such as raw or cooked, or ripe or unripened fruit will also influence the degree of toxicity.

One of our most recognized native poisonous plants is poison ivy (Toxicodendron radicans). Along with poison sumac (Toxicodendron vernix) and poison oak (Toxicodendron pubescens), poison ivy contains a toxic compound called urushiol. This oily substance can cause an allergic skin reaction by touching any part of the plant, whether it is alive or dead, resulting in a skin rash varying in severity from person to person. If possible, immediately after contact with the plant, wash your skin with running water rather than soaps containing oils as these may make the rash more widespread. The urushiol oil can remain active for months on objects, such as tools, clothing, and pet fur so anything coming in contact with the plant should be thoroughly washed with warm soapy water. Caution should be taken when burning the plants, as the oil particles in the smoke can be inhaled and cause lung irritation.

Poison ivy can be found growing as a single plant, a bushy or trailing shrub, or a woody, climbing vine. Its leaves are alternate and each leaf is made up of three leaflets with edges that may vary from smooth to sparsely toothed. Leaves have a reddish tinge as they emerge and mature into dull green before turning shades of red and purple in the fall. In the spring, 4-inch clusters of yellowish-green flowers appear and are followed by berry-like fruits that are round with a white waxy coating.

Poison oak grows as an erect shrub, typically 2 to 4 feet in height, but may grow as tall as 10 feet. Its leaves resemble those of a white oak tree and are alternate and made up of three leaflets with lobed or toothed margins. Loose clusters of small, white flowers appear in the spring and are followed by gray or tan berries, which have a velvety covering.

Poison sumac Is an erect shrub or small tree that may grow up to 25 feet in height. Its dark green, alternate leaves consist of seven to thirteen 2- to 4-inch-long leaflets arranged in pairs along a stem with a single leaflet at the end. The leaves are bright orange as they emerge in early spring, mature to dark green, and turn orange to red in the fall. Loose branching clusters of greenish-yellow flowers appear in early to mid-summer and are followed by round berry-like fruit that begin green and ripen to a yellowish-white in late summer.

White baneberry (Actaea pachypoda) Is an herbaceous perennial with erect stems growing 1 to 3 feet tall. Its leaves are made up of two to three deeply-lobed, sharply-toothed leaflets. Dense clusters of small white flowers bloom from April to June on tall flower stalks that rise above the foliage. The berries that follow are most often white but occasionally are red. When they mature, a prominent dark dot appears, which is the reason behind one of its common names, doll's eyes, as they resemble eyes used for dolls in the past. All parts of the plant are poisonous if ingested, especially the roots and berries. The berries contain a cardiogenic compound that can have an immediate sedative effect on the heart.

Water-hemlock (Cicuta maculata) is a large, highly branched, herbaceous perennial that may grow up to 8 feet tall. Considered to be one of North America's most toxic plants, it contains a clear, brownish resin called cicutoxin.  All parts of the plant are poisonous, but the roots are the most poisonous part, and ingesting even a small portion of the roots can be fatal. Its leaves may be made up of two or three leaflets that are lance-shaped and have coarse teeth around their margins. A distinguishing characteristic of its leaves is that the veins in the leaf run to the notches between the teeth. Its hollow, smooth stems may be tinged, mottled, or streaked with purple. Umbrella-like clusters of tiny, white, five-petaled flowers bloom in summer through early fall. 

Horse nettle (Solanum carolinense) is an herbaceous perennial that is not actually a nettle but a member of the nightshade family (Solanaceae). Growing up to 4 feet tall, its leaves are 2 to 4 inches long, lobed, and, along with its stems, are covered with fine hairs and spines. When crushed, the leaves smell like potatoes. Light violet or white, five-petaled flowers with yellow centers bloom in the summer and fall. The green berries that follow the flowers initially have the appearance of very small tomatoes, but they become yellow and wrinkled as they ripen. All parts of the plant contain the toxic compound solanine and are poisonous when ingested. The berries are the most toxic part of the plant, and the toxicity is often stronger in the fall as the poisons are more concentrated.

Cow parsnip (Heracleum maximum) is a short-lived perennial or biennial with leaves that are alternate and made up of three or more leaflets with three to five deeply divided lobes and serrated edges. The stems are hollow and covered with small hairs. In its first year, the plant forms an arrangement of leaves radiating from the base of the plant, and in its second year, a 4- to 15-foot flowering stem emerges with 6- to 8-inch umbrella-shaped clusters of small, white flowers. The sap of the plant contains furocoumarins. When this sap is exposed to the sunlight, it undergoes a chemical change producing toxins that injure the skin.  After touching the plant, sunlight may cause a painful blistering rash, and in severe cases, this may resemble a burn. All parts of the plant are toxic to the skin, so when working around cow parsnip, gloves and clothing should be worn to cover exposed skin. 

Pokeweed (Phytolacca americana) grows from large, 4 to 6 inch in diameter tap roots, and the plants may be 4 to 10 feet tall. Their large, elliptical, green, 3 to 6-inch wide leaves have an unpleasant odor when crushed. Blooming from July through September, its 3/4 inch wide flowers have five petal-like, greenish-white sepals that form 8-inch flower clusters with separate flowers attached to short stalks equally spaced along a central stem. As the flowers mature, they become pale magenta in color, and as the flowers change in color, so do the stems on the entire plant, from green to deep magenta. The flowers give rise to a drooping cluster of green fruits that ripen into purple-black berries. The plant contains saponin glycosides and the entire plant is poisonous. With knowledge and proper care, pokeweed has been eaten. However, it is not recommended unless strict procedures are followed to minimize its toxicity.  The root is the most poisonous and the leaves' and stems' toxicity increases as the plant matures. The berries are the least toxic, however, children are most frequently poisoned by eating the raw berries. Its juice can be absorbed through the skin so it is recommended to wear gloves while handling.

Virginia creeper (Parthenocissus quinquefolia) is a rapid-growing, woody, tendril-climbing, perennial vine that may grow to 30 to 50 feet long. Its leaves are made up of five elliptical, toothed leaflets arranged alternately on the vine. Small, green, inconspicuous flowers appear in late spring to early summer and are followed by dark-purple to black berries that mature in the fall but are typically not visible until autumn leaf drop. All parts of the plant contain oxalic acid and are toxic to humans. Ingestion may cause nausea, abdominal pain, and vomiting and may be fatal if the fruit is eaten. Contact with the skin may also cause an irritation similar to a mild case of poison ivy.

Common elderberry (Sambucus canadensis) is a woody, deciduous shrub that grows from 5 to 12 feet in height and is usually wider than it is tall. Its leaves are opposite and made up of usually seven, but sometimes five to eleven, leaflets that are 2 to 6 inches long with sharply serrated edges. Its bark is grayish brown, dotted with small brown bumps. Flat-topped or rounded, dense clusters of fragrant, white flowers bloom in late spring to early summer and are followed by clusters of rounded blue-black berries. All parts of the plant are poisonous and contain cyanide-producing toxins. Ripe berries are edible when cooked. However, they should be eaten with caution as some people with certain health conditions and on certain medications may be more sensitive to the toxin.

This is not a complete list of all of Pennsylvania's poisonous native plants. More information may be found in Cornell Cooperative Extension's Common Poisonous Plants publication. If you suspect poisoning, contact your physician immediately or the National Poison Control Center at 800-222-1222.