3 species & 1 hybrid in Australia
Rhizophora L. (1753) is a pantropic genus, and key member of the small family Rhizophoraceae R.Br., known as ‘the mangrove family’. The family consists of 16 genera and around 120 species of trees and shrubs. Four genera are found exclusively in the mangroves and these are conspicuously viviparous, including Bruguiera, Ceriops, Kandelia (DC.) Wight & Arn. and Rhizophora. These genera, and Rhizophora in particular, dominate mangrove forests around much of the world’s tropics. Rhizophora are distinguished from the other genera by their stilt roots, and flower calyces with 4 pointed lobes, 6-16 stamens, and the separate fruiting body and viviparous propagule. The genus consists of two broad regional groupings of species, including: the Indo-West Pacific ‘stilt’ mangroves, R. mucronata, R. stylosa, R. X lamarckii, R. X annamalayana Kathiresan and R. apiculata; and the Atlantic East Pacific ‘red’ mangroves. Rhizophora mangroves have similar shaped leaves but stilt species are readily distinguished from red mangroves by a prominent spiked, mucronate tip at the leaf apex, instead of a blunt recurved tip.
Derivation of Genus Name
‘Rhizo-phora’ means root bearing (in Greek), and refers to the characteristic stilt roots of this genus.
Rhizophora are widely distributed along tropical and subtropical coastlines from east Africa across to Asia, the Malay Peninsula and the Philippines to the western Pacific Islands, and northern Australia. All Indo-West Pacific species of Rhizophora are found in Australia, that is, except for the hybrid R. X annamalayana, present only in India and Sri Lanka.
Key to Australia's rhizophora species
Three species of Rhizophora and one hybrid are recognised in Australia’s mangroves across the northern coast from Western Australia, Northern Territory, Queensland and New South Wales. They are distinguished by cork wart spots on leaf undersurfaces, style length, petal hairiness, hypocotyl shape, and relative lengths of peduncles and petioles.