Many shrubs and trees we plant in our landscapes can be poisonous to humans and animals. Some are toxic if ingested and others may be irritating to the skin.
Following are four plants commonly found in Marco Island landscapes which most people would not think of as being poisonous. It’s best to exercise caution when dealing with any plant unless you’re completely familiar with it.
The yellow allamanda is a fast-growing vine. The 4” to 6” leaves are in pairs of three or four along the stems and the large yellow flowers are produced in clusters near the ends of the branches. The fruits are rounded, spiny pods approximately one-inch long. The plant is a native of Brazil but has become very common in Florida. There are many forms varying in flower size and color, leaf shape and the size of the vine. The plant is usually grown on a trellis but there is also a sturdier shrub variety. The bark, leaves, seeds and juice have been used for their laxative effect. The plant, especially the fruit, has the reputation of being dangerously poisonous.
The crown-of-thorns is a low growing plant with thorny stems and branches. The thick stems, about one foot tall, are purplish in color and covered with stiff, sharp spines ½” to 1” long. The leaves are few in number and mostly at the ends of new growth. The small flowers are long stalked clusters of 2, 4, 6 or 8 each with a pair of bright red bracts about ½” across.
Crown-of-thorn is a native of Madagascar. In Florida it is a popular specimen plant used for its year round color. The milky sap is very irritating to the skin of some people. The root contains a toxic substance and the plant has been used as a purgative.
The mango is a large evergreen, tropical fruit tree which grows to 60 feet tall. Its form is low and spreading. The dark green leaves are narrow and 6” to 16” in length and 1” to 2” wide. Young growth is reddish in color.
The small, yellowish flowers are produced in large clusters at the ends of branches. The fruits are large, 2 to 6 inches long, and usually asymmetrical.
The color can be red, yellow or green with a red spot. The yellow flesh is thick with tough fibers extending from the single seed outward toward the skin. The mango is native to India but can be found in tropical and sub-tropical regions around the world. It is related to poison ivy and so people sensitive to it may have similar reactions when coming in contact with the mango plant.
The few who suffer this irritation can have trouble when handling any part of the plant. Susceptible people may suffer severely around the mouth after eating fresh ripe fruit. Cooking destroys the irritating material.
The oleander is a woody shrub or small tree 5 to 25 feet tall. When allowed to grow naturally it will form a dense clump but can be trimmed to a single large trunk. The bark on young stems is smooth and green, but older branches and trunks are gray and rough. The leaves are 3 to 10 inches long, narrow, evergreen, leathery and pointed at the tip. The color is a dull, dark green. The flowers are produced all year in upright clusters at the ends of branches. The colors vary from white through pink, creamy yellow and rose to deep red. The seed pods are long, narrow, cylindrical and paired.
All parts of the plant exude a gummy, sticky sap when injured. All parts of the oleander are poisonous if eaten. One leaf is reported to be sufficient to kill an adult human. The dry leaves are almost as toxic as the green ones. Children can be poisoned by carrying flowers around in their mouths in play. You could also be poisoned by eating frankfurters roasted on oleander stems over an open fire at a picnic. Inhaling smoke from burning oleander can also cause symptoms of poisoning.
Contact of bare skin with any part of this plant can cause irritation. Poisoning symptoms include nausea, vomiting, colic, dizziness, drowsiness, decreased pulse rate, irregular heart action, bloody diarrhea, unconsciousness, respiratory paralysis and death.
While most people don’t chew on leaves and twigs from a shrub or tree they are unfamiliar with, small children might. Gardeners could very easily come in contact with the sap of these plants when pruning and not realize what caused the problem.
The Collier County Extension Office has more information in a pamphlet titled “Poisonous Plants around the Home.”
Eileen Ward and her husband, Peter, own and operate Greensward of Marco Inc., a lawn maintenance and landscaping company. Besides completing horticultural courses from the University of Florida, she has a commercial maintenance spray license and is a registered dealer in agricultural products in Florida.