A volunteer nature guide in Japan has discovered that a type of vine creates mini-greenhouses to warm its developing fruits. He has now co-authored a scientific paper describing the finding.
Schizopepon bryoniifolius is an annual vine that grows throughout east Asia, often on the edges of forests, and belongs to the same family as cucumbers, pumpkins and squashes. In the autumn of 2008, Nobuyuki Nagaoka noticed that some leaves on a S. bryoniifolius plant had expanded and overlapped with each other to form enclosures. Inside these were many developing fruits.
He noticed the same unusual structures forming again in the following autumns. Nagaoka eventually contacted Shoko Sakai at Kyoto University, whose team has now studied these vines on Mount Gassan in the Dewa Sanzan mountains in Yamagata prefecture.
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The researchers suspected that the enclosures acted as mini-greenhouses, so they monitored the temperatures in intact ones and in places where the leaves were removed. They found the temperatures in intact enclosures were up to 5°C higher at noon on sunny days, and also varied less.
They think the enclosures also protect developing fruits from frost damage, but they haven’t shown this. Far fewer fruits grew to more than a centimetre in diameter when the enclosures were removed. Plants at higher, colder sites also grew thicker enclosures.
“The results suggest that enclosures allow the plant to produce seeds under the cold weather the plant encounters at the end of its life,” the researchers write.
S. bryoniifolius isn’t the only plant that makes its own greenhouses. A species of rhubarb that grows high up in the Himalayas, Rheum nobile, forms hollow columns up to 2 metres high made of overlapping, pale-yellow leaves. It can be up to 10°C warmer inside these columns than outside.
Some other plants, such as Eriophyton wallichii, have woolly leaves to insulate themselves, while the petals of buttercups focus heat on the centre of the flower. A few plants, such as the eastern skunk cabbage, can even warm themselves by burning sugar to generate heat.
Proceedings of the Royal Society B
