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Colorful Coralbeans

January 21, 2010

Dangling limply from spindly dead-looking sticks, the bizarre pods of the Western Coralbean (Erythrina flabelliformis) wouldn’t look out of place in a Tim Burton movie. This tropical legume adds splashes of hot color to both winter and summer landscapes in a few counties along the Mexican border.

The orange-red color of coralbean seeds may warn animals of a potentially deadly snack. Potent alkaloids present in the seeds, bark, and roots can cause serious illness or even death in humans (an excellent reason not to grow this plant around small children!). These toxins have been used for centuries for killing pests and stunning fish, but natural poisons often have medicinal uses, too. In addition to many traditional uses, coralbean alkaloids have been employed as a muscle relaxant and in treatment of schizophrenia, and recent research has explored possible anti-cancer and antimicrobial activity.

The seeds are virtually armor-plated, with an outer layer so tough that it may take years of abrasion and/or freeze-thaw cycles to let in enough water to break the embryos’ suspended animation. To germinate them for the garden, we have to scarify the seeds with coarse sandpaper, nick them with pruning shears (very carefully! don’t want to lose a finger), or crack them with a hammer. This durability probably helped ancestral Erythrinas spread across the tropics, as seeds carried down rivers by seasonal floods survived the journey across thousands of miles of open ocean to germinate on distant shores. The Wiliwili of Hawai’i (Erythrina sandwichensis) and critically endangered Erythrina tahitensis are descendants of such seafaring seeds.

In the U.S., cold winter temperatures limit Western Coralbean to shrubby size and life on sun-baked rocky slopes, but in the tropical deciduous forests of western Mexico the plant becomes a tall, lanky tree. In late spring, whorls of knife-like scarlet flowers appear at the ends of the bare branches, attracting hummingbirds and orioles. The short-lived leaves emerge during the late summer “monsoon” to store a few weeks of solar energy for next year’s bloom season before turning from bright green to lemon yellow.

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