The black mangrove (Avicennia germinans (L.) Linnaeus) is a halophyte growing along both the Atlantic—Florida to Texas and Mexico south to Brazil—and Pacific coasts—Baja California to Ecuador. The shrub/tree can be readily identified by the pneumatophores arising from its extensive horizontal root system and the salt crystals on its leaves.

The black mangrove is found on slightly higher soils than the red mangrove (Rhizophora mangle) which is identified by its arching prop roots. The black tolerates the greatest fluctuations of the tides, inundation to drying. When the tide goes out, the salt concentration in the soil increases because of drying. Yet during rains, the soil is leached and the black tolerates decreased amounts of salt. The red mangrove grows where salt concentrations are relatively stable; the black where salt concentrations fluctuate with the tides and weather.

The black mangrove handles salt in two ways. The roots filter seawater removing 30 to 90 percent of the salt. The remaining salt is shunted to 'salt glands' in the upper epidermis of the leaves. These salt glands are microscopic depressions in the surface of the leaf and are composed of two to four basal cells, a stalk cell, and eight to twelve secretory cells.

The black mangrove blooms in early summer. The four-petaled white flowers have a yellow throat and are arranged in cymes. They remain open for several days and produce abundant nectar. The tree becomes a honeybee haven.

Each flower produces a single-seeded pod. The pods are retained on the tree until the seed germinates. Germination stimulates the pod to drop and open releasing the seed—actually two cotyledons folded over a thick radicle (first root). The cotyledons open like wings and the seed becomes a seafarer. The seafaring seed has about four months to land on appropriate shores and take root.

(Compiled from: Trees, Shrubs, and Woody Vines of Northern Florida and Adjacent Georgia and Alabama, Robert K. Godfrey, University of Georgia Press, Athens and London, 1988; "Avicennia germinans L." James A Duke, Handbook of Energy Crops, 1983, unpublished, posted on the internet by the Horticultural Department of Purdue University; "Salt Management in Avicennia germinans and Rhizophora mangle (Draft #1)", Malcolm Schongalla, 2002, posted on the internet by Interdisciplinary Studies of Miami University; and "Avicennia germinans (L.) L", Cristina Garibaldi, Reforestation, Nurseries and Genetics Resources, 2003.)