Rhizophora L.

Genus comprised of about 8 species of trees and shrubs, known as mangroves. They grow in tropical maritime coastal areas of most of the planet. Three species of the genus live in N Africa: R. mucronata, native to the Indian Ocean and the western Pacific, R. racemosa G. May. and R. mangle L. from both sides of the Atlantic. One more species has traditionally been considered in the Atlantic, but it seems to be a hybrid between R. racemosa and R. mangle, with which it lives: Rhizophora × harrisonii Leechm.

Living in salty, marine water, these species have developed aerial roots in the lower and middle parts of the stem, sometimes hanging from the branches of the crown. These roots have lenticels in the bark, they are connected to the spongy tissue inside, which allows the plant to store oxygen when it is underwater. Another surprising adaptation is its way of reproduction. The seed germinates in the fruit before falling, forming a very elongated propagule that sometimes exceeds 60 cm before falling into the water.

These species, along with other trees and shrubs, also with special adaptations to seawater, sometimes form dense and extensive forests of high ecological value: mangroves.

On the Mediterranean coasts, mangroves persisted at least until the end of the Tertiary (e.g. Sendra et al. 2000, Popescu et al. 2021) but with the succession of Quaternary glacial periods and the detour of warm marine currents, they disappeared from the Mediterranean and, across the Atlantic, following the Western Sahara coast, its area gradually moved towards the S. Currently the closest Atlantic mangroves forests are in Senegal, almost outside the geographical area of this project. The vegetation of the Atlantic African mangroves is dominated by 6 species of trees and large shrubs. The best represented are the red mangroves (those already mentioned from the genus Rhizophora, 2 species + their hybrid) and the white mangroves, here represented by the genus Avicennia, with the salty mangrove, A. germinans (L.) L. The other two less abundant species, of the Combretaceae family, are Laguncularia racemosa (L.) C.F. Gaertn. (Conocarpus racemosa L.) and Conocarpus erectus L.

In eastern Africa, the warm waters of the Red Sea have allowed, despite the ancient and intense humanization of these coasts, mangroves to remain much further north, but only with a few specimens and small forests of A. marina (Forssk.) Vierh., which reaches N to Sinai. Further south it is joined with R. mucronata, which to the N reaches the area around the Sudano-Egyptian border.

Updated by: J. Charco.