Rhizophora stylosa  Griff. 1854

pronounced: ree-ZOH-for-uh sty-LOH-suss

(Rhizophoraceae —  the mangrove family)

common name: Red Mangrove

Rhizophora rhizophora stylosa stilt rootsstilt rootsrhizophora stylosa flowerfloweris from the Greek  ριζοφορος (rhizophoros), root-bearing; stylosa is from στυλος (stylos), a pillar used as a support. This mangrove has stilt roots emerging in arches from the lower trunk, and extra prop roots often grow down from the branches.

The growth habits of this genus are more typical of mangroves than those of their cousin, the White-flowered Black Mangrove. Indeed, it is probably Rhizophora that the average North Queenslander pictures when he thinks of mangroves, as the seedlings are seen half buried in the sand and mud of most mangrove forests. The fruit of this mangrove does not fall off the tree when it ripens. Instead, the single seed within the fruit germinates when it is still on the mother tree, and the tree channels nutrients to the growing seedling, or vivipary. The seedling then forms a stem, known as a hypocotyl. When the seedling eventually falls, at rhizophora stylosa fruitfruitrhizophora stylosa budsbudsfirst it floats horizontally, and drifts with the tide. It can survive for long periods at sea. After some weeks, the tip gradually absorbs water, and the seedling floats vertically and starts to sprout its first leaf from the top, and roots from the bottom. When it hits land, it grows more roots to anchor itself upright, and then more leaves. The seedlings grow rapidly to avoid being submerged at high tide. They can grow by 60 cm in the first year. Because Rhizophora are fast growing, and sometimes flower within their first year, they are often used to replant mangroves either for conservation or as part of a managed forest to produce timber for construction or charcoal.

All species of Rhizophora have stilt roots, which not only hold up the tree in soft mud, but are also permeable to gases, while remaining impermeable to salts. In fact, the entire upper root system, including the trunk and the prop roots than come down from the branches, have this feature, and help the tree to ‘breathe’. At the root level, Rhizophora use a process called ultrafiltration to exclude salt. It is believed that they store any salt which manages to enter the plant in old leaves that are later shed.

The Red Mangrove, a small tree up to 8 m tall, occurs low in the intertidal zone, where its roots are submerged at high tides. There are considerable numbers of them between Cockle Bay and West Point. They are often to be found growing in sand as well as in mud, as they are better at resisting the surf than are many other species. Their bark is reddish or pale grey.

rhizophora stylosa propagulepropaguleThe opposite leaves are obovate to elliptic, 6–14 cm long, 3–8 cm wide, thick, glossy and glabrous, the lower surface usually spotted with reddish corky glands. On Magnetic Island, the species usually flowers and fruits in February. Each inflorescence carries between 2 and 8 flowers. These are small and white, with four petals of a distinctive shape, hairy at the ends, and four cream sepals angled at 45º to the petals, giving a star-like appearance to the flower. There are usually 8 stamens. These tiny flowers are wind-pollinating, producing lots of powdery pollen and no fragrance or nectar. They are also self-pollinating.

The fruits are 2–4 cm long, and the viviparous seedlings are usually 20–50 cm long before they fall.

The timber is dark red and fine-grained, quite difficult to work, but capable of a high finish. It has a very high calorific value, so it makes excellent charcoal, one of the heaviest there is. Charcoal making with this timber is carried on commercially in Indonesia, Malaysia, Thailand and Central America, and this, together with the extraction of tannin from the bark, has been responsible for large-scale mangrove removal and degradation. Red Mangrove charcoal is much used in barbecues, often in restaurants, where it not only burns with a high heat, but gives off a special aroma. It is also used in some industrial applications, like metal production.

Large sizes of timber are not often available, due to the relative smallness of the trees; but the grain is straight, strong, and extremely resistant to insects and rot. This makes it a very suitable timber for the building of Kelongs, the offshore platforms on stilts on which houses are built, especially in the waters off Malaysia, the Philippines and Indonesia. It is also exploited in some places for woodchip production, often on a large scale. In Australia, traditional uses for the timber include the construction of canoes, paddles, spears and boomerangs by the indigenous peoples. In New Guinea, it is used for making handles for high impact tools such as hammers, axes, and picks.

The caterpillars of several Lepidoptera feed on the plant, including:

• the Narcissus Jewel Hypochrysops narcissus;
• the moth Adoxophyes templana;
• the Copper Jewel Hypochrysops apelles;
• the Four-spotted Cup Moth Doratifera quadriguttata; and
• the moth Doratifera stenora.

 Photographs taken at Cockle Bay 2008

Page last updated 13th February 2018

 

 

 

 

 

 

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