Avicennia L.
Genus composed of 8 species of trees and large shrubs, known as white mangroves (as opposed to the slightly darker-leaved red mangroves of the genus Rhizophora).
The taxonomic position of Avicennia L. has always been controversial, ever since Endlicher (1841) separated it, to form the Avicenniaceae family with this single genus. This family has been traditionally included in the Verbenaceae as a subfamily, but it appears that its position must be within Acanthaceae, also as the Avicennioideae subfamily, given the uniqueness of its size, floral structure and habitat.
White mangroves are distributed throughout coastal areas of tropical and subtropical zones around the world. This particular salt habitat, variable due to the effect of the tides, is exploited by mangroves through special morphological adaptations, such as the pneumatophores that rise vertically from the ground, above water level, so that they can breathe oxygen despite the fact that other roots and the base of the stems are immersed in water. Furthermore they have a powerful system to eliminate the salt from the leaves and branches through their cells, like other species that grow is highly saline habitats of the Sahara (as in Amaranthaceae or Tamaricaceae). Another of its special characteristics is its viviparous reproduction. The seed germinates inside the fruit before falling from the tree. Once the fruit falls into the water, it has up to 4 days to open and release the propagule, which depends on the temperature and salinity of the water. Far from the river mouths, it is after the rains, when the salinity decreases, when the fruit opens allowing the propagule to take root in the soil.
Two species in N Africa: A. marina, from the Red Sea and Indian and Western Pacific Oceans, and A. germinans, from the Atlantic and Eastern Pacific Oceans. Under optimal soil, salinity and temperature conditions, together with other trees, mainly of the Rhizophora genus, they form dense and extensive forests in coastal areas, the mangroves.
Duke, N.C., Ball, M.C. & Ellison, J.C. 1998. Factors influencing biodiversity and distributional gradients in mangroves. Global Ecology and Biogeography Letters 7: 27-47.
FAO. 2007. The World’s Mangroves 1980-2005. FAO Forestry Paper 153. Forestry Department, Food and Agriculture Organization of the United Nations (FAO), Rome.
Marius, C. 1985. Mangroves du Sénégal et de la Gambie, écologie, pédologie, géochimie : mise en valeur et aménagement. Collection travaux et documents / ORSTOM. Paris. 357 pp.
Schwarzbach, A.E. & McDade, L.A. 2002. Phylogenetic Relationships of the Mangrove Family Avicenniaceae Based on Chloroplast and Nuclear Ribosomal DNA Sequences. Systematic Botany 27: 84-98
Key to species
1 Yellow or yellowish flowers. Indian and Western Pacific Oceans Avicennia marina
1 White flowers, only yellowish or orange in the throat. Atlantic and Eastern Pacific Oceans Avicennia germinans
Updated by: B. Valdés & J. Charco.