The gray or white mangrove, Avicennia marina, is found worldwide in tropical and subtropical climates. It is one of the best Acanthaceae medicinal herbs. Researchers are increasingly interested in mangrove ecosystems, including those dominated by A. marina, because they can produce bioactive phytochemicals like phenolics, flavonoids, saponins, sterols, terpenoids, tannins, and glycosides. A diverse group of salt-tolerant plant species have adapted to the extreme conditions of the mangrove ecosystem, where they must deal with fluctuating tidal levels, high soil salinity, and limited oxygen. The phyllosphere, the aboveground habitat of plants, hosts a rich and diversified microbial population driven by local environmental conditions and plant-specific traits. A. marina, a prominent mangrove species, has a distinct bacterial population in its phyllosphere, with different mangrove plant species having variable numbers of bacteria and fungi. All of these made the mangrove ecosystem a prospective source of novel bioactive natural products, although A. marina’s bioactive chemicals and biological activities are still being studied. Due to environmental limiting variables or habitats, mangrove bioactivity varies.