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The Leguminous Trees (Of Chennai)

The Leguminosae, a family of flowering plants exhibiting a great diversity of habit and floral organisation, so diverse that it necessitated a trifurcation, viz., papilionaceae (Fabaceae), Caesalpinaceae and Mimosae, is the third largest with as many as 600 genera and 12,000 species. Yet, the family is characterised by the kind of fruit all of them bear, called legume. The legume is one-chambered with the seeds located on a marginal placenta, - placenta, incidentally is a mass of cells which sustain growth (of seeds, in this case) - with its dry pericarp (fruit wall) breaking up along its two longitudinal sutures (the places where the two halves of the fruitwall are joined together).

In many of them, the pericarp after suffering extreme dehydration breaks up quite explosively, curling and twisting, in the process causing a loud report while the seeds inside are thrown out over long distances. It is a mechanism devised for seed dispersal in order to prevent seedlings overcrowding in a small area and competing for the limited amounts of water and mineral nutrients.

Long back, sometime in the mid-50's I think, as I was lazing in my chair near a window in the Department of Botany of Pachaiyappa's College, I heard sounds like so many pistol shots. Naturally I was woken up from my reverie, dying with curiosity about the sounds, their origin and nature. Looking out, I could fix the source, Gliricidia maculata, an exotic tree that came to the Indian landmass from the Caribbean Islands. Looking out from near the window, I couldn't determine the exact cause of the sounds. So, I ventured out, in spite of the heat of that summer day and looked up at the tree. The fruits were bursting open at the margins, the now separated halves of the pericarp were curling and twisting outward, with the seeds getting shot out to long distances. One seed, I could locate nearly 100 metres away from the tree. That was a moment when I felt happy about the choice of my study - Botany! The Gliricidia is in flower during January-February of the year and just before flowering, it sheds almost all its leaves and consequently the pale pink racemes of flowers stand out very conspicuously, reminding one of the Japanese cherry blossom. The Gliricidia is a medium-sized tree and its leaves make excellent rich green manure.

Our farmers, therefore, will do well to grow these trees on their field bunds. They do not require any extra care and without much effort the agriculturist harvests a rich mass of green manure.

Gliricidia means rat-destroying and the seeds seem to possess this power. Maculata means spotted and refers to the small glands present on the lower surfaces of the tree's leaves.

This is a commonly seen tree in all parts of Chennai, but you are likely to notice it only when in flower. If I chose to talk about Gliricidia first, it is because of that memory of pistol shot sounds that I still hear, after all these years. Gliricidia is a member of Papilionaceae.

But by far the most gorgeous of the Papilionaceous trees seen in Chennai is the coral tree, botanically christened Erythrina indica. The coral tree is one of India's own trees growing along the coastal and inland districts, in the deciduous forests. When in flower, this 'kalyana murungai' (its Tamil name) presents an unforgettable picture: its scarlet red flowers with a regular aviary of crows, minahs, babblers and green parrots hovering around them. These birds are there to feed upon the nectar inside the flower. It is one of those ornithophilous tree species pollinated by birds.

While the birds probe the flowers for nectar, their hard sharp beaks are likely to injure the staminal filaments and styles of flowers (structures associated with the formation of fruits and seeds), a fact that might defeat the very purpose for which the flowers allure the birds, through their colour and nectar. In order that these structures are not injured irreparably, they have highly suberized walls, rendering them woody in texture. Soon, the peculiarly twisted fruits make their appearance.

Another interesting feature of this tree is that it has a smooth bark, curiously streaked with vertical lines of green, buff, grey and white. And what is of extraordinary interest to us is that its trifoliate leaves are employed in the treatment of venereal buboes, inflammatory swellings of lymph nodes, especially in the groins amd armpits. In the compound of a house opposite mine, in Anna Nagar, there is a kalyana murungai tree.

Belonging to the same sub-family, viz., papilionaceae (Fabaceae) as the two that we covered so far, are the Pongamaram and Agathi tree. Botanically known as Pongamia glabra, The Pongamaram is an undertree that can be seen growing on the side walks of many roads in Chennai. This tree is given credit for the healthy breeze that filters through its foliage, and is proof of this common belief, I remember the grandmothers' prescription, tying a dry pod of Ponga Maram around the necks of youngsters suffering from that debilitating disease, the whooping cough Of course, the triple antigen dose administered to children as part of child health care has effectively countered that bacterial disease. 

Agati Maram, botanically known as Sesbania grandiflora was till a few years ago a very commonly grown tree in the backyards of many a home in Chennai. The leaves of this tree constituted a 'must' in the food consumed on the twelfth day of every fortnight (Dwadasi) as it is widely believed that the protein-rich leaves would compensate for the nutritional loss suffered by the preson who was on the fast on the eleventh day of every fortnight (Ekadasi). What with the practice of the fortnightly fast that had almost disappeared from observance in most Hindu houses, I am not surprised that the tree has almost disappeared from the backyards of many houses in Chennai. However, Agati leaves are sold by the vendors of greens and are much sought after by the housewives who seem to know their nutritive value instinctively.

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Today, however, Agati maram is grown as a windbreaker around banana gardens and also as a support to betelvine. The rural communities around make a tasteful dish from the large, whitish flowers of the Agati. I feel sorry that this culinary delight has disappeared from the Chennai houses. One can onlu feel helpless over such things.

There are other papilionaceous trees of some importance such as Dalbergia latifolia, the rose-wood tree. This is a huge tree, its trunk yielding a valuable timber, generally known as Rosewood. Rosewood furniture is a highly prized item in many houses. If I remember right, there was one Rosewood tree in the Agrihorticultural gardens on Cathedral Road, but alas! it seems to have fallen a victim to the woodcutter's axe, in the course of creation of a garden restaurant in the grounds. I don't recollect coming upon a rose-wood tree in all my wanderings through the city that I came to love, notwithstanding its nerve-racking traffic and the high deterioration in the living conditions.