More interesting mangrove plants...



Adult sea hollies

Young sea hollies

Unlike some mangrove plants, Sea Hollies (Acanthus Ebracteatus) do not exclude salt at the root level. In fact, their sap is salty and excess salt is secreted through the leaves, to be removed by rain or wind. Sometimes, the salt can be seen as a white crystalline layer on the upper surface. The plant produces a cluster of flowers that develop into pods. When the pods ripen, they explode to propel the seeds up to 2m away. Sea Hollies grow on mud near the hide tide mark, often on mud lobster mounds. It can grow equally well under trees and in open areas. But it grows especially well in areas with more freshwater input. The plant can sometimes cover large areas and form thickets, particularly in disturbed mangrove. They also grow along river banks.

Terantum Merah

The Teruntum Merah (Lumnitzera littorea) is a nationally endangered mangrove tree from the family Combretaceae. This tree can be seen at several of our mangrove forests, including Pulau Tekong, Pulau Ubin, Pulau Semakau, Pasir Ris, Sungei Buloh Wetland Reserve, Kranji and St John's Island. It occurs on the landward fringe of mangrove forests. The bark is fissured and reddish-brown. It relies on its roots to exclude salt from entering the plant through a process called ultrafiltration. It has simple, alternate, narrowly-drop-shaped leaves with a rounded tip. There is a small notch at the tip. The flowers are red and occur in clusters. They are strongly scented with lots of nectar.

Fish Poison Tree

What did I find most interesting on this walk? The Fish Poison Tree! The poison can stun the fish.  Doesn't this remind you of anesthesia??

The Fish Poison Tree is a large tree that grows on sandy and rocky shores. It has large leaves held in circular arrangement at the ends of the branches.  The young leaves are bronze colour with pinkish veins.

The flowers are like puff balls of white stamens tipped with pink.  They open at night, attracting large moths and nectar-feeding bats with their scent.  The next morning, the flower stamens are usually found strewn beneath the tree.

The fruits have a lantern shape and can float on water.  The fruit can survive drifting on the sea for long distances and for up to 2 years!  The outermost layer of the fruit wall is green, turning brown when ripe.  The middle layer is spongy and contains air sacs to help the fruit float.  The innermost layer is hard and thick to protect the seed.  The layers of spongy and hard coverings are similar to the coconut.

 All parts of the tree contain a poison called saponin.  The seeds and other parts of the plant are pounded, pulped or grated to release the poison and used to STUN fish in freshwater streams.  What a great way to catch fish!!  Don't worry, you will not die from eating the fish caught by this method because the poison will fade away after a few minutes. 

Threats to the ecosystem

Sadly, the interesting sights at Labrador Park were spoiled by the presence of rubbish pollution (unfortunately I did not take any pictures of the rubbish) that was clearly caused by inconsiderate people - plastic bottles, glass bottles, milk cartons, planks of concrete, straws and strings along the side of the creek where they just shouldn't have been.  And to think that this was only what we could see, not counting all those things at the bottom of the creekbed, and all the detergents and submerged weeds fed by human pollution or even acid rain?  This is obviously too much for Mother Nature to purify.  The deadly combination of human waste to feed the algae and stagnant water areas caused by rubbish piling up on the riverbed would allow substantial algae growth, which would take even more oxygen out of the mangrove soil.  The algae may even prevent the germination of new plants if the situation gets very serious.

To solve this problem, there is no short cut - the only way to prevent the destruction of mangroves would be for everyone to play a part and make a conscious effort to abstain from throwing waste into the sea.  Everyone may only have a small part to play, but precisely because of this, it takes everyone to make a difference, and everyone must play their part.  I'm glad we all consciously made the effort not to leave any rubbish behind...

Red Mangrove Fruit aka "the javelin"

The Red Mangrove Fruit in mid-germination

The red mangrove plant faces seed dispersion challenges similar to those of the boxfruit which I mentioned in my earlier post.  However, the innovative fruit uses a completely different method of seed dispersal.  After all, who said a seed had to wait fifteen long years to germinate when it could simply do so on its parent plant?  Well, that is exactly what the red mangrove fruit does. Once fertillised, it would germinate and begin to grow a vertical dormant root straight towards the ground while still on the parent tree.  Once the parent tree decided that this root was long enough, the fruit would drop off and hopefully onto muddy soil, where it would pierce straight in like a javelin.  This ensures that the "plantlet" does not get washed away by the tidal currents and germinates as an independent plant almost immediately.

The floating boxfruit

A second example of a plant with unique survival features is the floating boxfruit.  As its name suggests, this unique fruit is shaped like a box.  Like all other mangrove plants, it faces the extra challenge of having to avoid falling straight into water and getting drowned or getting washed away before it can germinate during high tide.                            

A decomposed box fruit we found on land - notice the fibres of the fruit?

What it must have originally looked like

As a result, the boxfruit has come up with a solution that fits its circumstances perfectly, even using the rapid change of tide levels to its advantage.  Covered in a non-porous, smooth and hard skin and its seed covered with a 5cm thick layer of spongy fibre, it is extremely water-resistant and bouyant.  In fact, it has the ability to stay alive afloat for 15 years, by which time it should have been washed ashore.  The only ingredient it would then need would be a soaking in rainwater.  This method of seed dispersion by water is similar to that of the coconut.

The roots of the mangrove plants

Our experience at Laborador park was memorable, as it was both an outdoor science lesson and an eye-opener for us.  Together with a tour guide, we walked along a trail leading us up a creek – from where the creek met the salty sea, up to where the mixture of salty seawater and fresh water from the mountains beside was more equal.  Although there were numerous interesting “survival features” of the plants we saw there, one of them clearly stood out even more than the rest. 

Firstly, the roots of the mangrove plants.  I’m sure everyone knows about these, but why are they needed in the first place?  Well, this is because, as mentioned earlier, the mangrove swamps’ water is salty, especially near the ocean.  In fact, this factor alone would cause a normal plant to die in less than a week!  What mangrove plants do is to keep the salt out, through means such as preventing salt from entering their roots and secreting salt out through their leaves.  However, the mangroves’ roots also have to cope with two other stresses – rapid tide level variations, which are enhanced upstream, as well as the lack of oxygen in the soil. 

Pencil Roots

Prop Roots

  To adapt to this, mangrove plants have developed prop roots and pencil roots. As shown above, prop roots are like a normal plant’s roots that have been pulled above ground, and pencil roots like sticks sticking out of the ground vertically.  Prop roots focus on keeping the plant sturdy amidst water movements, although stilt roots may later grow down when the plant gets older.  Pencil roots, on the other hand, focus on obtaining oxygen from the air, but the circles in which they grow still give a plant enough support.

Introduction

On 17 May 2012, 5I of ACS(P) went for an excursion to HortPark and Labrador Park. We saw lots of interesting plants and a couple of animals. Our group (Group 3) came up with a blog (This) to tell you about what we saw and our thoughts and feelings.

When we started the excursion, we went for a talk in HortPark. They told us about the many animals in Singapore, some which are endangered, others common. They also told us about how the National Parks started. We found out that, surprisingly, even as Singapore’s population nearly doubled over the years, the amount of greenery increased significantly. We then had a Q&A session before heading off to Labrador Park.