B. gymnorhiza is one of the two species of mangrove found in Mauritius. Its bark is dark grey to brown and is covered in lenticels (pores that allow gas exchange). The tree can grow up to 18 meters or more. It has dark green oval leaves with pointed tips. The base of the trunk bears buttress roots, which grow upwards and form arches. Flowering occurs year-round and pollination is done by insects and small birds. Its propagule is thick, tapering, smooth and relatively short in contrast to other species of mangrove trees. Once mature, it will drop in the mud and easily form a new tree.
Mangrove trees form the basis of mangrove ecosystems, sheltering a high diversity of fauna and flora among its roots and throughout its canopy, and providing food to many critters that inhabit them. Mangroves are found in upper intertidal areas of tropical coasts, in sheltered locations. B. gymnorhiza tolerates variable salinity and is often found along with Rhizophora mucronata. Mangrove ecosystems like other intertidal ecosystems have distinct species zonations that are determined by the elevation of the substrate relative to mean sea level.
B. gymnorhiza is one of the most widely distributed species of mangroves, which makes it a species of ‘Least Concern’ in the IUCN Red List. Unfortunately, it is threatened throughout its range by extraction and coastal development and has experienced a 20% decline since 1980. The impacts of climate change through rising sea water is likely to affect species zonation in its ecosystem. Locally, mangroves have often been destroyed to make way for coastal development. Fortunately, mangrove plantation programmes are being implemented in different regions.
The roots of B. gymnorhiza form “knee roots” and serve to develop new shoots, in addition to the fruit of the tree.