Causonis Japonica: Flowers With Amazing Changing-Color Ability

Causonis japonica, a plant native to Japan, is the first to exhibit the newly discovered trait. Its flowers can change color depending on the stage of maturation, then return to their original color.

Although many flowers have been shown to change color as they mature, Causonis japonica is the only known example of bidirectional color change.

Because the pigments involved in the colors are related to nutrient-rich, colorful vegetables, understanding the color-changing tricks of flowers could have downstream applications in improving nutrient yields in specific food crops.

Flowers show their true colors

(Photo : Sergey Shmidt/Unsplash)

We all like flowers, and one of their most appealing aspects is presumably their variety of shapes, sizes, and, of course, colors, as per ScienceDaily.

But did you know that some flowers have the ability to change color? Although not all flowers exhibit this trait, it has been observed in hundreds of different species for at least several decades.

Color-changing flowers are thought to do so because they signal to pollinating insects that the flower is ready to supply nectar or pollen, which rewards them.

This is regarded as an "honest" signal. However, some plants exhibit a "dishonest" signal, with some of their flowers displaying their default color while others display their signal color.

This behavior is thought to increase the plant's overall visibility to potential pollinators from a distance.

However, regardless of the plant's strategy, all examples of color-changing flowers discovered were unidirectional: once the color changed, it did not change back.

Imagine Hirokazu Tsukaya, a University of Tokyo professor, being surprised to see a flower of the plant Causonis japonica change color, and then change color again and again.

Despite having studied this plant extensively since discovering at least two varieties in 2000, the bidirectional color-changing flowers were a completely unexpected discovery, according to Tsukaya.

My colleague Professor Nobumitsu Kawakubo from Gifu University is an expert in time-lapse, long-period video recordings of pollinating flowers, and he and his student originally tried to explore the pollinating behaviors of different types of Causonis japonica, expecting to see the familiar change from its default orange color to bright pink.

You might have noticed that the chemical name carotenoid sounds similar to the word carrot. It's no coincidence that the same chemical gives carrots their orange color.

It's a good source of vitamin A, and given that the color-changing flowers show the most rapid accumulation of carotenoids ever seen, it's no surprise that the researchers believe their discovery could be useful in developing carotenoid-containing vegetables that mature faster or contain higher yields of beneficial vitamins in the future.

Attracting pollinators

The majority of New Zealand's native flowering plants are pollinated by animals, most notably insects but also birds and bats, as per the Science Learning Hub.

Plants provide nectar and pollen to animals as edible rewards for visiting flowers.

When an animal reaches into a flower for its reward, it brushes up against an anther, and some pollen adheres to its skin.

When the animal visits another flower, some of the pollen falls onto the stigma, indicating that pollination has occurred.

Animal-pollinated plants' pollen has a rough surface to help it stick to a pollinator.

Many flowers use color to entice insects, which is sometimes aided by colored guiding marks. Some have ultraviolet marks that insects can see but are invisible to humans.

Flowers are frequently shaped to provide a landing platform for passing insects or to make them brush up against anthers and stigmas.

The phutukawa (Metrosideros excelsa) makes use of color in a unique way. It has very small petals but large, bright red stamen clusters.

Some flowers contain scents that attract insects. Many of these scents are pleasant to humans, but not all; for example, some flowers attract flies with the odor of rotting meat.

Because colors cannot be seen in the dark, scent is essential for flowers pollinated by night-flying insects such as moths.

Grasses, as well as some of our native trees and shrubs, such as beech (Nothofagus species), kawakawa (Macropiper excelsum, pepper tree), and many Coprosma species, are wind pollinated.

Wind pollination is sporadic at best. The wind may pick up pollen from a grass flower and disperse it throughout the area.

A small amount of pollen will fall on another flower of the same species by chance. Wind-pollinated flowers produce a large amount of pollen to compensate for this waste, as hay fever sufferers are aware.

Wind-pollinated flowers typically have small, dull-colored petals, or no petals at all in the case of grasses. They do not require petals, color, nectar, or scent to entice animals.

The pollen grains are not sticky like those found in animal-pollinated flowers, so they are less likely to stick to leaves and other obstacles.

Receiving flower stigmas are sticky in order to catch pollen carried by passing breezes.