A Hydra-headed plant

by Geetha Ramaswami

 

When Lantana was brought to India, people didn’t realise that it would soon become a formidable weed in our fields and forests

 

Hercules, a hero from Greek mythology, was given the task of defeating a vile monster – the Lernaean Hydra. The Hydra’s venomous breath did not allow any creature to live, and it replaced one chopped head with two more! This story is about a real life Hydra.

Have you noticed a bushy plant with hairy, fragrant leaves and thorny branches in your backyard? You might have plucked its beautiful pink or orange flowers and sucked on the nectar at the bottom or feasted on its sweet, juicy, purple-black berries. If you know this plant, then congratulations! You have met the Lernaean Hydra of the plant world and it is called Lantana.

Invasive plant

Humans have a habit of moving things around, including plants and animals. We put creatures in places where they have not been for millions of years. Some of them thrive, spread and displace other plants and animals in their new homes and these are called ‘invasive species’. Lantana is an invasive plant, which was brought from South America to India in the early 1800s as an ornamental garden plant. Little did the bringers of this plant know that it was soon to become a formidable weed in our fields and forests. Lantana grows so thick that it often forms a ‘wall’ along roads and shades out the seedlings of forest plants. Wild animals don’t eat Lantana and it may replace a lot of useful plants, including grasses (that animals do eat) in forests. In the past 200 years we have tried cutting, burning and uprooting it, but to no avail.

How is Lantana so weedy?

Like the Hydra, chopping off Lantana’s head only makes it sprout a few more instead. In a grown Lantana plant, a ‘meristem’ that produces roots and shoots is hidden away under the soil. Cutting or burning Lantana above the soil surface triggers the meristem underground to produce many more stems from new shoot buds. In effect cutting or burning a Lantana stem only makes it bushier!

Every Lantana bush produces hundreds of berries. Some seeds get swallowed by birds and travel far away from the mother plant. Birds void these seeds in new places starting a new cycle of infestation.

When no one eats the berries, the seeds inside fall to the ground and get stored in the soil under the mother plant in a ‘seed bank’. Because Lantana came to India very recently, microorganisms and larvae of insects have not learnt how to eat up or to infect lantana seeds. Uprooting a grown Lantana plant exposes buried seeds to light. In the place of one grown Lantana, there appear hundreds of tiny plants, many of which become full-grown within a year (imagine a Hydra who could sprout a 100 heads in the place of one)!

Hercules had to deal with only one Lernaean Hydra, but forest managers and farmers have to deal with hundreds of Lantana plants every day. For now, we are left with the Herculean task of constantly watching and removing Lantana plants as they appear, and repeating this for a long time to come.

 


 

Lantana is one of the most weedy woody shrubs in the world and apart from India, is a big problem in Australia, South Africa and Hawaii

The orange or pink coloured Lantana flowers turn yellow when pollinated (usually by butterflies and sometimes by tiny creatures called thrips).

It is very dark under a Lantana bush – sometimes only 5-10% of sunlight may reach the soil under a thicket of Lantana; and this makes it hard for other plants to grow there.

Lantana can produce toxic chemicals that don’t allow other plants to survive and grow.

 

This article appeared in the Hindu in School on 26 November 2014.

Illustration: Lantana is like a monster, gobbling up native habitats and species.
Credit: Geetha Ramaswami