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Bakau (Malay)
Rhizophora spp.

stilt rootsAll Rhizophora species have arching stilt roots that emerge from the trunk, hence their scientific name Rhizophora which means "root bearer" in Greek.

These roots 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 prop roots that emerge from the branches have this feature. Thus the roots also help the tree to breathe.
Mangrove and wetland wildlife at
Sungei Buloh Nature Park
stilt rootsMain features: Grows 15-25m tall.

Roots: Stilt roots emerging in arches from the lower trunk, and prop roots may grow downwards from branches.

Leaves: Tiny black spots on the underside of the leaf.

Flowers:
Flower inflorescence long, slender and yellow. No scent or fragrance, wind-pollinated.

Fruits: The seed germinates in the fruit forming a seedling.

World distribution: East Africa through coasts of the Indian Ocean to Southeast Asia, China, Australia, Melanesia, Micronesia.

Classification: Family Rhizophoraceae. World 8 mangrove species.
Rhizophora use ultrafiltration at the root level to exclude salt. It is believed that they store any salt that gets through in old leaves which they later shed. Rhizophora grow best in wet, muddy and silty sediments.
The tiny flowers are wind-pollinated, producing lots of powdery pollen and no fragrance or nectar. They are also self-pollinating.

germinating seedling on the treeThe fruit does not fall away when it ripens. Instead, the single seed within the fruit starts to germinate while it is still on the mother tree, and the mother tree channels nutrients to the growing seedling (vivipary). The seedling forms a stem (called a hypocotyl).
seedling growing in the mud
When the seedling finally falls, at first 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. Rhizophora seedlings grow rapidly to avoid being submerged at high tide. They can grow by 60cm in the first year.

Because Rhizophora are fast growing and 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. The other mangrove species used in replanting mangroves are Avicennia and Sonneratia.
Rhizophora found in
Sungei Buloh Nature Park


leaf and red leaf stipuleBakau Minyak (R. apiculata): leaf stipule and leaf stalk reddish. Flower inflorescence short, stout, dark grey.

young seedlings Seedlings shorter (30cm), slender with a smooth skin and grows slightly curved with a rounded tip. More restricted distribution, only Southeast Asia and Micronesia.

Bakau (R. stylosa) and
Bakau Kurap
(R. mucronata): In both, the flower inflorescence is longer, slender and yellow, the seedling is longer (60cm) and has a warty bumpy surface. The flower of R. stylosa: has a longer style (4-6mm). R. mucronata is more widespread and also found in East Africa where R. stylosa is not found.

Role in the habitat: see mangrove trees.

Status and threats: R. stylosa is listed among the endangered plants in Singapore, but it is common elsewhere.

LINKS
REFERENCES
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Nature's Niche
  • Peter K L Ng and N Sivasothi, "A Guide to the Mangroves of Singapore I: The Ecosystem and Plant Diversity", Singapore Science Centre, 1999 (p. 126-133: description, habit, photo.
  • Michael Mastaller, "Mangroves: The Forgotten Forest Between Land and Sea", Tropical Press, 1997 (p. 28-30: about the roots; p. 34-35: about how seedlings disperse and sprout; p. 97: medicinal uses).
 
By Ria Tan, 2001