River mangroves commonly grow as a shrubby hedge along river banks
The river mangrove Aegiceras corniculatum belongs to the family Myrsinaceae. The species is distributed throughout South East Asia, and extends from southern New South Wales along the east coast of Australia and along the west coast from Cape York to Shark Bay.
It is a common mangrove of southern Queensland, occurring along banks in the upper tidal reaches of creeks and rivers where it is frequently encountered as an understorey beneath stands of grey mangrove. It may also form pure, dense stands in the centre and landward zones of mangrove forests.
River mangrove grows on poorly drained mud that is periodically inundated by saline or brackish water.
River mangrove occurs as a bushy shrub 2 to 3 m high but may occasionally grow to a small tree with several slender trunks up to 6 m high.
The bark is rough and dark grey or black.
Leaves are spoon-shaped with a rounded tip, and are glossy green above and paler green below. They occur alternately along the stem, while the surface is covered with minute salt glands that excrete salt from the plant.
Clusters of white flowers may appear with a smell similar to rotten bananas.
Roots along the soil surface are exposed to air at low tide and help the uptake of oxygen. Prominent lenticels (air pores) at the base of each trunk also help with atmospheric gas exchange.
Salt encrustation on the leaves is an identifying feature of the river mangrove.
Flowering and fruiting
Most flowering occurs in late spring and early summer with minor flowering all year.
The single-seeded fruit is small, curved, elongated and fleshy, and appears between summer and autumn. Seeds germinate on the tree (vivipary).
Healthy plants can tolerate fresh and salty water. Salt is extruded by glands on the leaves, which accumulates over time resulting in a fine film of white salt crystals on leaf surfaces. These crystals are most often seen during prolonged dry weather and are the primary characteristic by which river mangrove can be identified.
River mangrove trunks were used as stakes in the culture of oysters and the trees are still a major source of pollen for beekeepers. This species provides valuable habitats for juvenile commercial and recreational fish, and is suitable for the rehabilitation and stabilisation of river banks and estuaries.