Synopsis

Land plants surround us, but there’s a parallel world that is largely hidden: water plants. They create some of the most beautiful, bizarre and important habitats on earth. In this episode we see Sir David Attenborough explore the water worlds in Croatia, Kew Gardens, London and the River Avon in Wiltshire.

Life in water is tough. In a torrent, just holding on takes extraordinary innovation. The brilliantly coloured plants of Colombia’s Rainbow River stick to rocks with nature’s version of super-glue.

In Brazil’s flooded Pantanal, plants battle for a place in the light. They travel with dangling roots, use air-bags to stay afloat and reproduce fast. But in the end there’s only one winner. The Giant Water lily emerges from the depths, armed with spikes, to shunt, crush and stab the opposition.

The Marimo, a perfect sphere of alga, uses the water currents of its Japanese lake to roll to the perfect spot. Too deep for predatory swans, but shallow enough for sunlight, it gathers in strange colonies of thousands.

In Brazil, plants find one river so much to their liking that they make visible the process that creates our atmosphere. Their internal chemistry, called photosynthesis, works at such a rate that bubbles of pure oxygen stream from them, filling the river like uncorked champagne.

When flowering, water plants become, for a time, like land plants, sending flowers into the air on rigid stems. The result is some of the most beautiful flower spectacles on earth.

Fresh water covers a tiny proportion of the land surface. Finding it is challenging for a seed, so the bullrush produces a quarter of a million and releases them slowly, increasing the chances that, on one day at least, the wind will blow them in the right direction.

Just one flowering plant has made it into the sea: Sea Grass. These submerged savannahs not only support a huge amount of animal life, they also absorb carbon dioxide 35 times faster than tropical forest. Now threatened, they are vital in the fight against climate change.