Leaving home: How seeds find their way into the world

Many plants use what I call ‘bribery and corruption’ to send their progeny away. They will cover their seeds with sweet, fleshy fruit, garbed in attractive colours (red, orange and yellow are favourites) and tempt animals and insects and birds to take a bite… Some animals will enjoy the fruit – and spit out or discard the seed (like the mango), others will ingest the seed which will journey through the animal or bird’s digestive tract and then emerge (far away from home, and sometimes in a more suitable if smelly condition for germination) as a dropping or in poop. Birds like barbets and hornbills are, in fact, responsible for afforestation in this manner.

Some seeds are covered with soft fleshy structures called elaisomes, which harvester ants love. So they take them underground, bury them, remove the elaisomes, and leave the seeds in their ‘garbage dumps’ – dark, fertile places perfect for germination. The silver arrowreed, (Ceratocarym argenteum) of South Africa cons dung-beetles (dumb-beetles here!) into believing they are delicious balls of dung, which the poor beetles take away and bury, futilely laying their eggs on them. Squirrels famously bury large hoards of seeds – like acorns – and forget where in many cases, enabling the seed to germinate. I have myself, enjoyed a mango and casually buried the seed in the garden and forgotten all about it. Today, the resulting tree is tall, dark and handsome and which hopefully should produce its own mangoes next year.

Some plants and trees – like the apple for instance – use gravity. They will drop their fruit (in the case of the apple, on Newton’s head who then went on to ‘discover’ gravity itself!) so animals and humans can easily pick them up and consume them.

Just as there are some youngsters who refuse to leave home and need to be forcibly booted out, there seem to be some seeds with the same attitude. So their parent plant builds up the pressure (usually hydraulic) inside the seed pod to such an extent that it explodes, scattering the seeds far and wide. The Himalayan balsam is one such, but apparently the champion is the sandbox tree, native of Central America which can blast its seeds away at speeds of 160 mph and cause bodily harm if you get in the way!

Coconut palms famously lean towards the ocean on beaches in order to drop their huge nuts into the sea and send them on voyages across the oceans, to far-away shores. They can float for months, nurtured by the nutrients packed within. I came across a travel-stained coconut on a beach in Goa, and wondered where it had set out from. The water lily releases its seeds underwater – they float upright for a while, moving away from their parents before settling down in the mud and sinking in their roots.

Then there are what I call the ‘hippie’ seeds, which though armed fearfully with hooks, barbs, spikes and burrs will quietly attach themselves to any passing animal (or human) and hitchhike, to be taken far away on foot or by car or even air.

Many seeds are deliberately taken by us from one place to another and become crops – and, others may occasionally become an ‘invasive’ species running roughshod over the local flora and wrecking the ecosystem. The lantana is one such. But we really can’t point fingers at any of them, considering we ourselves have become the world’s most ruthless ‘invasive species’ in all the major continents, during the last few hundred years, virtually eliminating native populations. Parent plants’ reasons for sending away their young are bona-fide – ours historically – patently mala-fide.