12 January 2009

Amazing Avicennia marina at Semakau

Avicennia marina is considered rare in Singapore. On the mainland, there is only one known patch with about 10 trees. Elsewhere, there are three at St. John's Island, one in Pulau Pawai and one off Pulau Tekong. Of these, the ones at Pawai and Tekong aren't doing very well.
I saw this tree on an earlier visit to Semakau and I thought it might be 'A. M.' as the Mangrove People call it.

Dr Jean Yong confirmed this is NOT Avicennia marina. It is actually a rather stressed Avicennia alba. He explains, with illustrations as we walk along the mangroves, that Avicennia alba can have rounded leaves, stunted fruits and other variations in forms due to growing in the shade of a bigger mangrove tree, or the water being too salty, or a lack of nutrients or the pneumatophores being buried and so on. His explanations really opened our eyes to the wide variety that common mangrove trees can take. Wow.

But we KNOW there is at least one Avicennia marina on Pulau Semakau. Ali Ibrahim found it during the Semakau Mangrove Survey in Jun 2005. So we push on to find it.

And lo and behold, THREE of them were found. The first and third ones were rather sad and bedraggled and Dr Yong believes they are not long for this planet.But the second one was in great health! The tree looked just as happy as Shufen. Of course, the Mangrove Paparazzi descended upon this precious little tree to document it. The tree is actually considered quite tall for an Avicennia marina. Most 'A.M.'s elsewhere hardly get above thigh or knee-height. So we shouldn't trample small trees in our mangroves! They could be grown up rare trees and not small trashy young trees.
This is definitely an 'adult' tree as it has 'fruits' (I think the correct botanical term is 'mature' tree') . These have a gorgeous tinge of blue and have a shape that is quite different from the other common Avicennia species. Now I can see why the local name for Avicennia marina is Api-api Jambu.The much talked about squarish stems are obvious here. And Dr Jean Yong points out the squarishness extends all the way down the stem and not just near the growing tips. The leaves are in various shapes from long to oval, and whitish. Leaves are not really a good distinguishing feature as the leaves of Avicennia alba may also have similar variations, though they are usually much whiter underneath than Avicennia marina.The bark of Avicennia marina is flaky, a mottled greenish yellow and peeling in patches. And the pencil-like pneumatophores are very very long and pointy.The flowers appear in this typical cross-formation.And the flowers are quite large and are said to be sweetly scented.

Shufen and I were so worried for the poor little tree as it was draped with dried up Sargassum seaweeds. We wanted to clear up the seaweeds. But Dr Yong quickly pointed out that as the seaweed, as it rots, provides valuable nutrients and minerals that the tree needs. We might only do this if there was so much seaweeds that the tree was bent over with the weight. Again, this shows that nature's way is best and that even with best intentions, we should not interfere. WOW!

From Tomlinson, P. B. "The Botany of Mangroves" (1986), Avicennia marina has a wide distribution both in latitude and longitude. It may be considered the most widely distributed mangrove tree, being found in East Africa and the Red Sea through the Indian Ocean and South China Sea, much of Australia into Fiji, and south to the North Island of New Zealand.

Tomlinson lists 7 variations and highlights that "Several varieties have been recognized, but morphological distinction is never clear cut and much of the segregation is geographic. Therefore, in the absence of precise morphometry on populations in widely separated localities and the recognition of other characters, it is impossible to provide keys with reliable diagnostic features."

This search for 'A.M.' has been exhilirating for all of us. And we are very grateful to Dr Jean Yong for so patiently explaining the finer points of 'A.M.' identification in the Singapore context!

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