This is a leaf from "Erythrina herbacea", native to Florida and the Southeast U.S. Note that the leaf has three leaflets, each with a thickened region of petiole at the base. This "leaf joint" is called a pulvinus. The pulvini bend and twist during the course of the day and reorient each leaflet with respect to the light and thermal environments. Changes in shape of the pulvinus are the result of osmotic changes in pulvinar cells caused by ion pumping.
Notice how the leaf is trifoliate - three leaflets - just like that of the common bean. Not surprising, though, since Erythrina is a member of the Legume family, just like the common bean. (However, not all legumes have a trifoliate leaf, many have finely divided leaves. But all legumes are characterized by a "legume" - the bean-like seed pod.)
There are approximately 110 species of "Erythrina" worldwide, most in the tropics. The "Erythrina" is prized as a ornamental tree since most species have showy flowers. The most common flower color is red or reddish-orange, hence the name - Coral Tree. But a species native to Hawaii and Tahiti has white flowers! The flower shown here is that of "Erythrina herbacea".
The seeds of over 40 species of "Erythrina" contain alkaloids - So, it might be a good idea not to stuff any in your mouth!
But, I am most interested in the orientation of leaflets with respect to light sources. Most species of "Erythrina" show daily heliotropic movement of leaflets (helio = sun, tropic = orientation in response to a vector stimulus). Typically, one can characterize leaf or leaflet orientation as diaheliotropic, where surfaces orient perpendicular to the rays of the sun, or paraheliotropic, where surfaces are "edge-on" to the rays of the sun. Typically, orientation is nearly paraheliotropic near noon, when the light flux is intense, and nearly diaheliotropic in the early morning and late afternoon, when light flux is low. At night, heliotropic plants move leaves or leaflets into a vertical orientation, the so-called "sleep" orientation. Technically this is known as nyctinasty (nyctinic = dark, nasty = position in response to a scalar stimulus). The following cartoon was drawn by our secretary, Shibuya-san, during my 1983 sabbatical visit to the Mitsubishi-Kasai Institute of Life Sciences, Machida-shi, Tokyo. Notice that the sleeping leaf is snoring ... In Japanese, snoring is "ku, ku, ku" as evidenced by the three Hiragana characters.
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All text and images not attributed to other are Copyright, 1997, Thomas J. Herbert. They may not be used for any commercial purpose without the express written permission of Thomas J. Herbert.