When winter’s dreariness settles in around us and we readily choose a warm spot by the fire rather than venturing outdoors, we rely on our houseplants to bring the world of nature into our lives. While houseplants serve us so well in this capacity, we would be remiss if we overlooked the fact that there are some common houseplants that can be potentially poisonous.

The term "poisonous" designates many kinds of reactions or effects, the majority of which are non life-threatening. Among the key effects are allergic reactions (caused by spores, pollen, or naturally occurring volatile compounds emitted into the air by plants), skin rashes or dermatitis (caused by direct or indirect contact with allergenic or irritant compounds), skin photosensitization (caused by exposure to irritating or allergenic compounds), and internal poisonings or irritations (from ingestion of plants or plant parts).

The general types of poisoning and examples of plants responsible for each are: blood poisoning (wild cherry, Prunus spp.), nerve poisoning (mushrooms), cardiac poisoning (foxglove, Digitalis purpurea), and skin irritation (poison ivy, Toxicodendron radicans). According to Dr. Sharon M. Douglas of the Department of Plant Pathology and Ecology at the Connecticut Agricultural Experiment Station in New Haven, recent studies estimate that 3.5% of all poisonings in the United States are due to plants.

A common houseplant that can be poisonous is Dieffenbachia, also known as Dumb Cane. It is a tall, erect plant with large oblong leaves splotched with ivory markings. The leaves are toxic, the chewing of which produce immediate intense pain followed by swelling of the mouth making it difficult to speak, thus the common name Dumb Cane.

Joining Dieffenbachia in its familiarity is the Philodendron, a climbing vine with aerial roots found in many homes. The leaves are large and variable, the most common being heart-shaped. The leaves are poisonous and when ingested cause painful burning of the lips, mouth, tongue and throat. Contact dermatitis may also occur.

Another houseplant that many of us are very familiar with is the aloe (Aloe vera). This succulent-type houseplant with its rosettes of thick, fleshy, stiffly upright leaves is found on many windowsills. The poisonous parts are the cut leaves that, if ingested, may cause nausea, vomiting, diarrhea, abdominal cramps and heart palpitations. A common folk medicine belief is that the sap of the cut leaves is good for soothing burns and various other kinds of skin irritations. I have used the sap of aloe in this way for years and have always received some measure of relief for minor skin irritations However, dermatitis has been reported, and according to the USDA Natural Resources Conservation Service, episodes of burning skin following topical application of aloe gel have been documented.

The next two houseplants are perhaps more potentially dangerous, especially for children, because of their alluring colors. The first is the Jerusalem Cherry (Solanum pseudocapsicum). It is an attractive, interesting plant that bears many colorful round orange, yellow, red or black berries that resemble cherries. The entire plant can be poisonous especially the berries which children can find very inviting. When ingested, the berries cause gastric irritation and fever, diarrhea and a scratchy feeling in the throat. They may also cause a rash if they come in contact with the skin.

Angel Wings (Caladium bicolor) is another colorful houseplant that can pose a danger. It has large, showy, variegated, heart-shaped leaves patterned in green, white, pink and red. Intense irritation of the lips, mouth and throat occurs when any part of the plant is ingested.

Contrary to popular belief, one houseplant that is not poisonous is the perennial holiday favorite, the poinsettia. The American Medical Association's Handbook of Poisonous and Injurious Plants lists nothing more than occasional vomiting as a side effect of ingesting otherwise harmless poinsettia leaves. According to the Poisindex Information Service (a resource used by most poison control centers), a 50 pound child would have to eat between 500 and 600 leaves to exceed experimental doses. According to California producer Thom David, poinsettia leaves taste far worse than the most bitter radicchio. Frankly, he says, the flavor is indescribably awful. So go head and enjoy your holiday poinsettias for as long as you can, not as an afternoon snack, of course, but as a welcome splash of holiday color during the drab days of late January.

For more information about potentially dangerous houseplants, click on the U.S. Army Center for Health Promotion & Preventive Medicine website at www.apgea.army.mil/ento/PLANT.HTM. If you want to learn just about everything you ever wanted to know about plants, check out the USDA Natural Resources Conservation Service Plant Links website.

Read other articles on care of house plants