MANGROVE or MANAWA
Mangroves grow on coastal and tidal mud flats throughout many tropical and subtropical parts of the world. In some places they form forests which yield important quantities of firewood. The family contains only the one genus, Avicennia, in which there are about 10 species. The New Zealand species is endemic and forms the dominant vegetation found on coastal mud flats north of latitude 38° S. It is a low shrub or small tree usually growing to little more than 20 ft under favourable conditions. Branchlets and leaves, which grow to a length of 2–3 in., are opposite and are clothed in closely appressed white or buff hairs. The leaf shape is elliptical
One of the characteristics which seems to enable mangrove to grow in such a seemingly inhospitable habitat as tidal mud flats is the presence of “breathing-roots”. These are erect, stout growths arising from the lateral roots and are exposed at low tide. They are composed of a spongy tissue and their function is to absorb air – hence the common name of breathing root.
The fruit is a large capsule with a single seed, and germination and root growth begin before it drops from the plant. When, therefore, the seed does drop, it quickly becomes established in the mud and is not subject to constant movement by tides.
by Alec Lindsay Poole, M.SC., B.FOR.SC., F.R.S.N.Z., Director-General of Forests, Wellington.