Deep in the dense forests of Central Africa, a forest fruit known as Pollia shines brightly, resembling the decorative lights of a Christmas tree.
According to Gizmodo, the Pollia fruit is dubbed the brightest organism in the world due to its ultra-microscopic structural composition. In reality, this fruit does not contain blue pigments as it appears. It is the fruit of the Pollia Condensata plant, which reaches a height of nearly 50cm and primarily grows in Ethiopia, Angola, and Mozambique.
The Pollia fruit resembles a Christmas tree ornament. (Photo: Discovery Magazine).
The surface of the Pollia fruit is made up of four thick layers of cells. Each layer consists of multiple sub-layers formed by intertwined cellulose fibers. All the fibers in a layer run parallel to each other, but the layers are slightly twisted around each other, creating a spiral shape when viewed from above.
When light strikes the surface of the fruit, the rays are reflected back and forth by each layer of fibers and are amplified through a constructive interference effect, producing vibrant colors that make the Pollia fruit brighter than any other organism on the planet. However, this fruit has no nutritional value.
According to physicist Silvia Vignolini at the University of Cambridge, UK, who studies the coloration of the Pollia fruit, the reflective effect occurs from both directions, left and right, of each cellulose fiber cell. This characteristic is quite unusual compared to the single cells of any ordinary object. The color-changing phenomenon of the Pollia fruit attracts various birds and animals to nest in the trees.
Pollia condensata, sometimes referred to as marble berry, is a perennial herbaceous plant with a branched stem and hard, dry, shiny, round metallic green fruit. It is found in the dense forests of Africa. The blue color of the fruit is created by structural coloration, the most intense compared to any known biological material.
In countries like Ethiopia, Mozambique, Tanzania, and Ghana, marble berries have long been famous for their shiny, eye-catching appearance, but it was only in recent years that scientists discovered what makes them so vibrant. A group of researchers at the University of Cambridge, seeking plants that can bend light in interesting ways, accidentally discovered a marble berry at Kew Gardens in the UK. It had been brought there from Ghana in 1974, yet over time, it has retained its impressive original color.
This plant was first described in Angola, in southern Africa. It has wide, smooth, narrow leaves and pale pink or white flowers on a stem about 60 cm tall. The capsule fruit has a diameter of about 4 mm.
In fact, plants with shiny colors typically rely on pigments to create their appearance, and over time, as they gradually degrade at the cellular level, these colors also fade and disappear.
However, the marble berry is an exception; despite the passing decades, their colors remain unchanged. This is because the color of this fruit is not produced from usual pigments; instead, it comes from a unique cellular structure that can reflect light and create stunning visual effects.
Researchers at the University of Cambridge (UK) found that the cells in the Pollia condensata fruit are made from light-reflecting cellulose fibers. The varying distances between the fibers in each cell reflect different wavelengths of light, resulting in the brilliant blue color.
Scientists refer to this type of color as “structural color.” It can be observed in various animal species, notably in peacocks, which have brown feathers that reflect light to create blue, turquoise, and green colors, as well as in some butterflies and beetles. Some plant species also exhibit structural coloration, but the marble berry is the most impressive example in the plant kingdom.
When analyzing the marble berry under a microscope, scientists discovered that the outer layer of the fruit consists of three to four thick-walled cell layers, each containing multiple layers of cellulose fibers arranged in a spiral pattern. When light strikes the berry, some of it is reflected. Essentially, the reflected light beams amplify each other to create this stunning shimmering blue color.
Structural color has previously been observed in animals, such as peacock feathers, beetle shells, and butterfly wings, but they use different structures and materials to achieve their unique effects. The Pollia condensata is the first case discovered in plants. Unlike pigments, structural colors do not fade over time, as the structure remains intact even when absorbing light.
In addition to simply reflecting light of specific wavelengths, the helicoid structure of this fruit also alters the light of other wavelengths so that the wavelengths converge within a narrow range before being reflected, effectively amplifying the light at that specific wavelength. This constructive interference process creates the strongest color of any living organism. The total reflectance coefficient is about 30% of that of a silver-coated mirror, the highest compared to any known biological material. The rich colors make the fruit attractive to certain bird species, even though it has no nutritional value. Sometimes, these birds decorate their nests with the berries, which over time helps disperse the seeds.
