Understand ballistic seed dispersal

BBC Wildlife features editor Ben Hoare explains ballistic seed dispersal. 

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Common gorse exploding seed pods.
Illustration by Dan Cole/The Art Agency

 

Of all the ingenious ways in which plants spread their seeds, ballistic dispersal is the most dramatic. “It’s a mechanical process in which seed pods detonate, firing their seeds away from the parent plant,” says botanist Trevor Dines of Plantlife.

The seed pods gradually lose moisture as they ripen, which builds up tension in their cells and thus in the pod as a whole. Eventually the structure fails and gives way, triggering an explosion. “Heat stress often provides the final kick,” Trevor says – which is why you’ll notice the phenomenon on hot days.

Gorse and other plants that use ballistic dispersal invest more energy in their individual seeds, which tend to be large and don’t travel far. By contrast, plants such as dandelions that use the wind produce lots of tiny seeds able to colonise new areas further afield.

Flowering

Gorse is among the few British plants to bloom every month, though peak displays are March–June. Its flowers smell of coconut, pineapple and almond – like piña colada! They’re edible, too…

Ripening seed pods

Mature flowers develop into thick, bristly pods about 20–25mm long. The outer cases stiffen and blacken as they ripen in the sun. The green spines deter deer and other browsing animals.

Exploding seed pods

On hot days the ripe pods finally burst with an audible crackle. It’s a classic summer sound of heathland, commons and verges. Each pod flings four to eight orange-brown seeds up to 3m. They are much larger than seeds dispersed by the wind.

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