A Toxic Trio

 

Wild Poinsettia (Euphorbia cyathophora).
Palm Beach County, Florida. 

Florida, with its subtropical climate, has an array of fascinating plants.  It also has more than its share of invasive species from all over the tropical world.  Orchard View Park in Delray Beach has a mix of native and introduced plants. Three of these plants stand out because they are visually striking but also poisonous.

Air Potato (Dioscorea bulbifera) leaves.
Palm Beach County, Florida. 

 

A single heart-shaped leaf of Air Potato.
Palm Beach County, Florida.  

An Air Potato bulbil.
Palm Beach County, Florida. 

Air Potato (Dioscorea bulbifera) is a vine native to Africa, Asia and Australia.  It is classified in the true Yam family, the Dioscoreaceae.  These yams should not be confused with Sweet Potato (Ipomoea batatas) which is in the Morning Glory family, the Convolvulaceae.  Air Potato was introduced to Florida in an Orlando area botanical garden in 1905, but it escaped and is now found throughout the peninsula. This vine rambles over bushes and grows high into the trees.  It has shiny, heart-shaped leaves and a stem that produces large, potato-like structures called bulbils.  Air Potato plants make several physiologically active compounds including the steroid diosgenin.  Diosgenin is the starting material for several medically important steroids including contraceptives.  While the Florida Air Potato is considered toxic, other varieties around the world are used for food, but the bulbils must be boiled before eating to make them safe.

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Crab's Eye (Abrus precatorius) leaves
and dried fruits containing seeds.
Palm Beach County, Florida. 

Another toxic invasive plant in the park is Crab’s Eye (Abrus precatorius).  This member of the Fabaceae, the Pea family, has compound leaves and the peapod-like fruits contain the seeds that give the plant its name.  The seeds are brilliant red with large black spots like the eyes of some fever dream crab.  The bright seeds are used in some tropical countries to make beads, giving rise to another common name, Rosary Pea.  But these seeds contain abrin, a toxic protein.  Abrin is so poisonous that consuming a single seed can be lethal.  The seeds of this plant are sometimes used as means of suicide in India where the plant is native.  Crab’s Eye has been introduced to tropical and subtropical locations worldwide.   

Wild Poinsettia flowers and leavers.
Palm Beach County, Florida. 

The third toxic plant in the park is Wild Poinsettia (Euphorbia cyathophora).  The Wild Poinsettia flowers are small, yellow and green.  These flowers are set off by the bright red and green bracts below the flowers. Wild Poinsettia is native to tropical and subtropical America and is naturally found in Florida.  It is a close relative of the ubiquitous Poinsettia of Christmas fame (Euphorbia pulcherrima).   The stems and leaves of Wild Poinsettia contain a white, milky latex that can cause contact dermatitis, eye irritation and in rare cases of anaphylaxis.   

Fruits and seeds of Crab's Eye.
Palm Beach County, Florida. 

Since plants are rooted in the ground and cannot flee from danger, they must rely on other means to protect themselves from being eaten by animals.  One way they do this is to produce toxic compounds to protect themselves from hungry herbivores. The latex of Wild Poinsettia and the steroids of Air Potato are good examples of this type of chemical protection.  Even the deadly toxin abrin made by Crab’s Eye will cause gastrointestinal distress in low doses and discourage grazing animals.  I enjoy these plants and appreciate their protective adaptations but from a distance.  I definitely don’t eat them.