Avicennia have the highest salt tolerance of mangrove trees. They do not exclude salts at the root level. In fact, their sap is salty, at about one-tenth that of sea water. Instead, they secrete excess salt on their leaves through special pores, to be removed by rain or wind. Sometimes, the salt can be seen as a white crystalline layer on the upper surface of the leaf.To avoid suffocation in the oxygen poor (anaerobic) mud, they have pencil-like pneumatophores. These stick out at regular intervals from long shallow underground cable roots that spread out from the trunk to stabilise the tree.
The tiny flowers are hermaphroditic; female flowers producing sterile pollen while male flowers produce sterile ovules. Both types produce lots of nectar and fragrance to attract insect pollinators. Avicennia produces some of the best honey.
While the seed does germinate on the mother tree, the growing shoot does not penetrate the seed coat while the fruit is still on the tree (thus this is called cryptovivipary). The shoot and roots only appear after the fruit falls off. And these grow best in water of the right temperature and salinity.
Because Avicennia species regenerate branches easily from their trunk, it is possible to harvest branches without hurting the tree and maintain mangroves for such harvests (called coppicing). Avicennia is among the few used in replanting mangroves to protect coastlines (the others are Sonneratia and Rhizophora).
Role in the habitat: Being able to tolerate saltwater, Avicennia are among the first mangrove trees to colonise mud and sandbanks which are regularly flooded by seawater. Thus the trees stabilise the shores, preventing erosion and allowing other plants to grow.
API-API (Avicennia spp); SEJARAH SERTA KEISTIMEWANNYA Mac 3, 2010