Under this family, there are three tribes, Rhizophoreae, Gynotrocheae, and Macarisieae. Even though Rhizophoraceae is known for its mangrove members, only the genera under Rhizophoreae grow in the mangrove habitats and the remaining members live in inland forests.
The terrestrial members of the Gynotrocheae tribe include the genera Carallia, Crossostylis, Gynotrochea and Pellacalyx.
Within the mangrove tribe Rhizophoreae, there are four genera: Rhizophora, Kandelia, Ceriops, and Bruguiera, all of which are found in the coastal regions of Singapore.
So we will discuss here the characteristics of this tribe in general. There are three distinct adaptive characters known in this tribe
๐ทViviparous embryogenesis
Thisestablishes the seed embryo that starts growing while still in the fruit on the tree. It breaks the seed-coat and the fruit wall to grow large enough to take root in the slippery salty soils of the mangrove. This adaptation ensures propagation of the seed and avoids it being washed away with the coastal waves.
๐ทHigh salt tolerance
Growing in the salty intertidal waters, these plants have narrow and dense xylem vessels in the wood for optimum osmotic pressure and greater salt tolerance. This also prevents dehydration of the tissues. Some Rhizophoraceae plants also have salt glands that excrete excess salt from the plant.This adaptation is particularly useful in saline environments, where excess salt can accumulate and become toxic to the plant. By excreting salt through these glands, the plant can maintain a healthy salt balance and avoid toxicity.
๐ทAerial roots
Aerial roots are a unique feature of Rhizophoraceae plants that help them combat salt levels. These roots grow above the ground and provide structural support to the plant. They also help the plant breathe by providing access to oxygen since mangrove soils don't get enough aeration. Additionally, these roots secrete salt, allowing the plant to get rid of excess salt
Besides this the other features are
๐ทLeaves are simple, leathery, with entire margins, oppositely placed (but not decussate) Stipules are present.
๐ทAerial roots present in all members of Rhizophorae tribe but may not be present in other tribe members
๐ทFlowers are produced in terminal cymose inflorescences.
๐ทIndividual flowers are bisexual, actinomorphic, 4-5 distinct sepals and petals. Petals deeply bifid or fringed.
๐ทOvary usually inferior except in tribe Macarisieae where it is superior.
๐ทFruit is a capsule in Crossostylis genus of Gynotrocheae while in other tribes it may be fleshy berry like or drupe.
๐ทSome yield wood used for underwater construction and piling, and tannins are obtained from the bark.
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