Bakau Kurap (Rhizophora mucronata)

The Bakau Kurap (Rhizophora mucronata) is a nationally common mangrove tree from the family Rhizophoraceae.


This rather common mangrove tree can be seen at most, if not all, of our major mangrove forests, such as Pulau Tekong, Pulau Ubin, Pasir Ris, Mandai, Lim Chu Kang, Sungei Buloh Wetland Reserve, Kranji, Khatib Bongsu, Seletar, Pandan, St John's Island and Pulau Semakau, among others.


This tree often occurs in parts of the mangrove forest that are flooded by normal high tide. The bark is dark grey or dark brown, and prop roots and stilt roots can be seen at the lower part of the tree. These roots help the plant breathe air, which is scarce in the waterlogged soil. The roots spread over a wide area to help stabilise the tree on the unstable ground. Like other mangrove species from the family Rhizophoraceae, R. mucronata relies on its roots to exclude salt from entering the plant through a process called ultrafiltration.


It has simple, opposite, leathery leaves that are broadly elliptic with pointed tips, clustering towards the end of the branch. The leaf buds are cover by red or light green stipules.


Here are the ones with light green stipules.


Tiny black dots can be seen on the underside of the leaves, as in the case of other Rhizophora species.

Stalks of flower heads are long and forked 2-3 times, and 2-14 flowers on long individual stalks up to 5 cm long. The flower has a short style, 0.5-1.5 mm long.

The dull, brownish fruit is somewhat drop shaped.


Vivipary is observed in this plant, as with the other mangrove species from the family Rhizophoraceae. This is a condition whereby the embryo grows and break through the seed coat and the fruit wall while still attached to the parent plant. Hence, the thin and long structures seen hanging from the trees are the seedlings, not fruits. The hypocotyl can be more than 60cm long, rough and warty, with a pointed tip.


Mature seedlings are dispersed by water and have a light green or whitish collar. The seedling floats horizontally for a few weeks, during which the root (lower part) will absorb water and become heavier, eventually causing the seedling to tip and float vertically. As the tide goes down, the vertically-oriented seedling will sink into the mud or other suitable substrates. Most of the seedlings, however, end up being washed ashore or eaten by animals. As the seedlings are thin and long, many of them also ended up settling directly under the parent tree, as they drop and poke into the soil below.

The wood is hard and heavy, and is used for making charcoal. This tree is often planted along fish ponds to protect the bunds. The bark is rich in tannin, and is used for tanning and dyeing. A friend told me that the seedlings are used by some locals to cane naughty kids.

References

• Chong, K. Y., H. T. W. Tan & R. T. Corlett, 2009. A Checklist of the Total Vascular Plant Flora of Singapore: Native, Naturalised and Cultivated Species. Raffles Museum of Biodiversity Research, National University of Singapore. Singapore. 273 pp.
• Giesen, W., S. Wulffraat, M. Zieren & L. Scholten. 2006. Mangrove guidebook for Southeast Asia. RAP Publication 2006/07. FAO Regional Office for Asia and the Pacific & Wetlands International. Bangkok. 769 pp.
• Ng, P. K. L. & N. Sivasothi. 1999. A guide to the mangroves of Singapore 1 : the ecosystem & plant diversity. Singapore Science Centre. Singapore. 168 pp.
• http://www.mangrove.my/page.php?pageid=mangrove