More on Trees

Mimosae

So, now we go on to Mimosae, the third sub family of Leguminosae.

First to come to mind is the Velikaathaan - Prosopis juliflora - arrived from Mexico. About fifty years ago, it was not ubiquitous as it is now. It is an undertree with sharp prickles all over. It needs little attention and therefore serves well in waste land reclamation. Moreover, its prickles make it an excellent fence if closely planted, impenetrable even to rodents. Apart from the fact that its branches, trunk and all make good firewood, its pods are relished by goats. Its cousin, Prosopis spicigera which was quite common in Chennai in yesteryears, is the famed Shamivriksham, in whose branches the Pandavas left their arms wrapped up in a cloth, the bundle resembling a human corpse, before they went into King Virata's court to spend the year incognito, as per the conditions laid down by Sakuni before the start of that ill-famed game of dice which Dharma Raja played against Duryodhana and his minions.

Rain tree which is easily the most common avenue tree in Chennai is botanically called Samanea saman. A native of Central and South America, it is now well established all over India, not to say Chennai too. It is a fast growing tree, with a phenomenal turn-over of biomass. Anytime of the year, underneath and around the tree, you see huge heaps of fallen leaflets. No herbivore touches them nor do they undergo decomposition quickly enough, a process so essential to soil building. As fas as I can see, the only way in which the dry leaves of this tree can be got rid of, is to set them on fire. However, its twigs when green are lopped off by goat-rearers: obviously, the leaves form a good bellyful for the goats.

The Rain tree is gigantic, growing upto 16m tall with the main trunk about 4-5 feet in girth. The branches spread out in all directions bearing dense foliage, so much so, a nearly circular shade of almost 100 feet diameter is formed. A wonderful place to park your car!

The tree bears flowers almost all through the year but most abundantly, during May-July. They form clusters of a pale rose hue. The colour is that of the staminal filaments rather than that of the petals: indeed, this is a family trait. A curious feature is that in the centre of the head, as the cluster is technically called, is a large sterile flower, which houses nectar. Insects, mostly of the creeping type come in search of this sweet fluid, incidentally effecting pollination.

The tree exhibits sleep movements, as indeed most of the leguminous trees do: though of course, here these are very pronounced. During day time, the leaves are open with their outer faces towards the Sun. But come dusk time, the leaflets fold up against one another, such that the lower surfaces face outward, hanging downward. The whole tree has gone to sleep as it were! 

The pods have a sweet pulp and are fed to cattle and goats.

If you permit, a little digression, please: for it covers an aquatic mimosoid weed, Neptunia oleracea, not a tree. So interesting is what I am going to say, I am sure my readers will approve of this digression. It is about a spectacle I was a witness to. I go back fifty odd years. Shenoy Nagar was in the making. Where now you have a vegetable market in Shenoy Nagar on Pulla Avenue, there was a large sheet of freshwater, almost what you could call a pond. In those waters was growing a weed, what we botanists call Neptunia oleracea. One morning, as I walked around that sheet of water the plant was very visible from the eastern rim with all the leaves of that plant looking at the Sun, as it were. As I reached the western rim of the pond, it looked as if the plant had disappeared altogether. In the evening, the experience was reversed: from the western rim the plant was very visible but from the eastern side, the aquatic weed was not to be seen!

Who says the plants do not move! Do you think the digression was worth it? Such wonderful pictures have disappeared altogether from the city's limits. You've to go to the countryside to experience such visual delights.

One question that has been bothering me whenever I talk of Rain tree is why it is called so. But the name seems to have an attractive ring about it. Otherwise, why would Taj Connemara call one of its restaurants, Rain tree. Now to go back and pick up the thread, I sometimes wonder that the tree is called so because it provides shelter against rain. It cannot be, because experience tells me that under the tree you are likely to be drenched more, because the leaf-bearing twigs tend to stoop downwards with its leaves taking on a sleeping posture in response to the cloudy sky. In this orientation, rain water drips heavily. But over the years, I've come to notice that the tree incessantly rains leaflets, though some of these trees in the summer months of some years would have shed all its leaves. One therefore cannot classify this tree: as deciduous or evergreen. Such trees, I'm told are described as Semi-deciduous. May be, this Semi-deciduous nature of the tree contributes to the incessant rain of leaflets exhibited by them, for after all a Semi-deciduous tree is also a Semi-evergreen tree. I wonder if I guessed right!

Albizzia lebbeck, the Siris tree of which we spoke in the introductory section of this series is a tall tree, reaching upto 15m. Quite common in the years gone by, now you've to keep your eyes wide open to spot a Siris tree. There are a couple of them in the campus of Pachaiyappa's College and quite a few, in the campus of Loyola College too. In April, it bears innumerable heads of fuzzy, green and white flowers. Its stamens have long, pale rose-colored filaments with a silken feel. When summer comes, the leaves are shed and from the bare branches hang large, papery yellow pods. As the season advances, the seeds cut loose within the legume and through high winds of the season, they keep hitting the dry woody walls of the fruit, producing a rattling sound. Hence, the nickname of the tree, the child's rattle!

Have you heard of the Badminton Bak tree? The Kadamba, Anthocephalous cadamba of Rubiaceae is the real Badminton Bak tree. But a leguminous tree called Parkia glandulosa is also called by the same popular name, not unjustifiably. Parkia glandulosa is a native of Africa and is grown as a shade-giving tree in Chennai. If I recall correctly, there were about four or five of them on the G N Chetty Road, T. Nagar. Recently I saw one in Loyola College, just adjacent to the Life Sciences block. I didn't come across a reference to this tree in treatises dealing with Indian flora. Obviously the species is yet to ecise in India.

Last, we may talk of the several species of Acacia, growing wild in the scrub jungles around Chennai and as stray trees in the compounds of some houses in Chennai. Acacia arabica is the babul tree; called Karuvelam in Tamil. It is of moderate height. Its leaves are associated with a pair of sharp spines, on either side of the leaf base. The flowers are golden yellow. It yields a gum, which with the entry of the synthetic epoxyresins, has gone out of use. However, the tree has many uses; wood for making charcoal, logs for making agricultural implements, bark for tanning and finally, pods for making a black dye.

Other species of Acacia, quite common in Chennai, are Acacia farneciana (Kasturivel) and Acacia leucophloea (Velvelum). Some of the species of Acacia have medicinal value.

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One last piece, before we conclude this section, Leguminous trees. All leguminous plants enjoy a symbiotic association with a type of bacteria, called Rhizobium. These are to be seen as nodules on the roots of these plants. These bacteria have a unique capacity to utilise the atmospheric nitrogen to build up their proteins - a process called Nitrogen fixation. The leguminous plant itself gets to be enriched in terms of nitrogenous supply and thus come to have a rich content of nitrogen in their seeds. This is why the vegetarians are advised to consume legumes: Otherwise, they'll go protein hungry. Leguminous crops such as pulses are grown in offseason and on maturity their tops are harvested, leaving their roots with bacterial nodules in the soil. The cereal crop that is subsequently grown in that field will have richer nitrogen supply - a fact which is at the bottom of the agricultural practice, called Rotation of crops.