Huge begonia standing at almost 12ft is discovered in Tibet 

Begonias with striking blue leaves may represent a next step in plant evolution that puts them ahead of their ordinary green neighbours, researchers reported in 2016.

The blue colour results from a super-efficient form of photosynthesis that allows them to use light other plants reject.  

There are around 2,000 species of begonia, but the biological function of the bright blue sheen has mystified scientists for decades.

But the researchers said the leaves only develop this sheen when put in almost dark conditions – and in bright light the sheen slowly disappears.

The flowers use their unusual leaves to harness what little light there is.

The study, published in Nature Plants, rules out a previous popular hypothesis that it was to to deter predators.

‘The real novelty of what the begonia is doing is combining the light harvesting mechanism with the photonic structure – light is being both structurally manipulated and harvested with high levels of quantum efficiency within the same material,’ said Dr Heather Whitney from Bristol University.

‘I am not a physicist – we started this work on the biology side – but my photonics collaborators tell me this is highly novel and may throw up some very interesting possibilities if we can replicate this.’

The plants – including species commonly grown as houseplants or in gardens – have long been using a special form of nanotechnology called photonics to create structures in their leaves to help them harvest light.

‘We discovered under the microscope, individual chloroplasts in these leaves reflected blue light brightly, almost like a mirror,’ said Matt Jacobs, a PhD student at Bristol University.

‘Looking in more detail by using a technique known as electron microscopy, we found a striking difference between the ‘blue’ chloroplasts found in the begonias, also known as “iridoplasts” due to their brilliant blue iridescent colouration, and those found in other plants.

‘The inner structure had arranged itself into extremely uniform layers just a few 100 nanometres in thickness – or a 1,000th the width of human hair.’

Chloroplasts harvest sunlight and convert it into chemical energy for the plant, with light initially absorbed by membranes, called thylakoids, that assemble into large, variably-sized stacks. 

One reason for the flowers’ popularity is their ability to survive indoors without direct sunlight.

This is because many begonias grow beneath tropical forests, where the light reaching the ground may be a tiny fraction of that at the top of the tree canopy. Plants here need to scavenge every bit of light they can in order to survive.

The researchers looked at Begonia pavonina – found under the thick canopies of tropical forests in Malaysia. It has iridescent blue leaves due to unusual chloroplasts, known as iridoplasts, in its surface layers.

These contain regularly spaced stacks of three to four thylakoids that resemble a photonic crystal and strongly reflect wavelengths of light between 430 and 560 nanometres – accounting for the leaves’ blue iridescence.

They look very similar to the artificial structures commonly used to make miniature lasers that control the flow of light.

In the Malaysian forests, the small amount of light that reaches the plant’s leaves is mainly at the green-red end of the spectrum.

The iridoplasts concentrate these specific wavelengths onto the plant’s photosynthetic apparatus – increasing the efficiency of its photosynthesis by five to ten per cent. 

The researchers said the plant’s unique design – perfected by evolution – could be used in other plants to improve crop yields or in artificial devices to make better electronics.