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Why Swiss cheese plants are full of holes

Leaves of Swiss cheese plants are unusually perforated to help them avoid stress, according to a new study.

London: Leaves of Swiss cheese plants are unusually perforated to help them avoid stress, according to a new study.

Their familiar hole-riddled leaves allow the plants to capture sunlight more regularly helping them to survive in shady rainforests, found research by a US scientist.Commonly grown as house plants, they are found in the wild from southern Mexico to Colombia, the BBC Nature reported.

Many theories have been suggested for the unusual perforated leaves.

One is that the holes in the leaves allow the plants to resist hurricane winds, by letting the wind pass through. Another is that they allow better temperature regulation or water to run through the plants down to its roots.

Some have suggested the holes somehow camouflage the plants, hiding them from herbivores.

Research by Christopher Muir at the University of Indiana, in Bloomington, US, suggested that the holes are an adaptation to the plants` rainforest habitat.

The Swiss cheese plant Monstera deliciosa lives in the dark understorey of tropical rainforests. It relies on capturing unpredictable shafts of sunlight, known as "sunflecks", in order to photosynthesise for energy.

Muir questioned whether the sunflecks could explain the unusual leaf shapes so he used mathematical models to compare leaves with and without holes. He found that both leaf shapes benefit equally from the same amount of sunlight.

Although a leaf with holes will miss some sunlight, because it filters through the holes, solid leaves with the same surface area actually take up less space, so their access to sunlight is restricted.

Muir`s models revealed that a leaf with the same surface area, but riddled with holes, would contact sunlight more regularly because it takes up more space.

He suggested this regularity makes the altered leaf shape more reliable, causing the plant less stress giving it the best chance of survival.

But young Swiss cheese plants do not need holes in their leaves, according to Muir.
Monstera deliciosa grows differently at different stages of its life cycle. It is an epiphyte, or air plant, with aerial roots which attach to host trees, enabling it to climb.

The young plants are closer to the forest floor, where fewer flecks of sunlight reach. The poor quality of the light here means that holes do not benefit the plant, Muir predicted.

Only as the plant matures it grows taller, reaching parts of the understorey with more flecks of sunlight.

Then the leaves become larger, develop holes and are held away from the trunk, where they have a better chance of capturing the sunlight necessary to survive.

The study was published in The American Naturalist.