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Plant colony

You can buy a staghorn fern at any garden centre and grow it like a pot plant. But in the wild, the ferns grow in a way that’s changing our understanding of biological complexity. Latched onto branches of rainforest trees, staghorn ferns (Platycerium bifurcatum) evolved to live in colonies on Lord Howe Island off Australia’s east coast, with individual ferns fitted like puzzle pieces and working together to collect water for the benefit of all colony members. The level of job division is such that about 40 per cent of individuals forgo reproduction. Social colonies, with strict division of labour and reproduction, are nothing new in the animal kingdom, says Victoria University of Wellington biologist Kevin Burns. Social insects—bees, ants, termites and some wasps—are the best-known examples of colony-building behaviour, but it has also evolved independently in crustaceans (certain species of shrimp) and even mammals (naked mole rats). But Burns’ research describes the first time it’s been observed in plants. Colony-building behaviour, or eusociality, is the most recent of eight major evolutionary transitions to more complex life. Burns says eusociality is defined by colonies that include several generations of adults, and dividing labour and care for offspring co-operatively. Staghorn ferns may not fit the strictest definition, and are unlikely to have rigid job division like termites. “I suspect they go through a succession, starting off being a reproducer, then maybe a collector, and they shift as the colony develops,” he says. But the important point is that colony life is not restricted to animals. “Plants can walk that evolutionary path in the same way, without a brain—and that’s a huge leap forward.”

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