The versatile pungam tree survives in a wide range of environments and has immense socioeconomic value. It is a host plant to many butterflies, like the pea blues (Lampidesboeticus) seen here, and its flowers run a covert operation.
Pongamia pinnata (pea family - Fabaceae), pungam in Tamil and karanj in Hindi, is a medium-sized tree native to the Indian subcontinent with a range extending to southeast Asia and northern Australia. Commonly known as the Indian Beech Tree or the Pongame Oil Tree, it has been introduced to many areas outside its native range.
It survives in a wide range of environments, tolerating drought, heat, harsh sunlight, fire, wind, inundation and salinity. The species is associated with mangroves and naturally occurs along coastlines and rivers. It is a preferred tree species in afforestation efforts and is commonly planted along city avenues for shade and as a windbreaker in landscaping.
The pungam tree produces a flush of reddish-hued young leaves that turn dark green on maturing. The older leaves often fall prey to herbivory by insects, scarred by blotches, snaky mines and galls. It has a brief shedding phase in early spring, making it an almost evergreen tree. The tree is a host to a coterie of butterflies with imaginative names such as Awls, Sunbeams, Ceruleans, Pea Blue and even a Sailer. The larvae of these butterflies chomp through pungam leaves to complete their life cycle and metamorphose into adults.
The tree produces small fragrant flowers in shades of white, pink and purple with dark maroon collars. These flowers are less than a centimeter long, clustered in pretty inflorescences that appear in spring and summer.
Pungam flowers are largely pollinated by bees and wasps, which set off the most adorable explosion. Each pungam flower has a large petal with a nectar guide that is hooded over four folded petals. Two of these inner petals, called keel petals, conceal a bundle of stamens that are held in tension. When an insect steps on these petals seeking nectar deep within the flower, the movement trips a violent ‘keel explosion'. Much like a landmine going off, this explosion sprays the underside of the insect with a cloud of pollen. These pollen are carried to other flowers by the foraging insects, which leads to their fertilization.
The seeds of pungam occur in pointed oval pods and are extraordinarily rich in oil, which has been extracted as lamp-oil, lubricant and an insect repellant, and is being explored as a source of biodiesel. Various parts of the tree are also important in traditional and folk medicine across cultures, used to treat a range of diseases. The leaves are great for composting and the wood is used as fuel and for making tools.
On campus, pungam trees can be found in the patch of lawn overlooking the parking shed near the hostel side entrance.
