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A crown in the flower

by Siddharthan Surveswaran

When you pass through any wasteland in your locality you may notice a pale green plant with thick leaves and small purplish-white flowers. Some even grow this plant in front of their houses for religious purposes. This plant is calledCalotropis, and it is a widespread kind of milkweed, originally from Africa. When you pluck a leaf of the Calotropis plant a gush of milky sap or latex oozes out from the wound and therefore these plants are aptly named as milkweeds.

Milkweeds flowers are perhaps the most interesting of all the many kinds of flowers in the world. In general, all flowers have male and female parts. The male part is called the stamen, which consists of a long stalk upon which a small capsule is attached. This capsule is called the anther and it holds pollen grains, which are the male cells. The female part of the flower is called the pistil which consists of a tube, called the style, and a head-like structure, called the stigma. In other flowers the male and female parts are separate, but milkweed flowers are remarkable because the male and female structures are united into an elegant circular structure that looks like a crown. Isn’t that wonderful? Like a king and queen ruling from the same throne.

Pack of pollens

Now, the point of flowers is reproduction – getting the pollen grains of one flower to land on the stigma of another so that fertilization can happen and the next generation (that is, the seeds) can be formed. Many plants use wind to disperse their pollen grains to neighbouring flowers, while other plants attract insects, which carry the pollen grains to other flowers. The clever milkweeds manage this more efficiently by packing their pollen into little bags called pollinia. (The only other plants that do this are orchids.) These pollen bags are embedded into the crown of the flower.

Why so complicated? When a bee comes to visit the milkweed flower for nectar it tramples on the crown and releases the pollen bags which then readily stick to the bee’s legs. The pollinia now hitch a ride with the bee, which visits the next flower for its next dose of nectar. The pollinia then land on the stigma of another flower and the milkweed fruits are formed.

The awesomeness of milkweeds doesn’t end there! Their seeds have a whisk of silky hairs attached to their head. These hairs catch the wind and carry the seeds like a parachute, dropping them off in distant places. This mechanism is responsible for the spread of these plants over long distances thereby colonizing newer and newer areas. Isn’t it amazing that these plants are so clever? Next time you see a milkweed plant, take a closer look. But be sure to wash your hands carefully after you touch the plant: its milky latex contains toxic substances to stop animals from eating it. The wonders of the humble milkweed go on and on!

This article appeared in the Hindu in School on 28 April 2015.

Picture: Flowers of the Calotropis plant. Can you see the crown in the centre of the flowers, with their five anthers?
Credit: Mayur Y. Kamble

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