When we go to the flower market, we always see some black flowers. These black flowers may not be popular compared to red and yellow flowers, but when we get closer, the price is very high.
This is because these black flowers are almost all from artificially cultivated varieties and are not common in nature, so the prices will naturally be higher.
The flowers of various colors in the flower market, including black flowers.
Recalling carefully, you may realize that we have almost never seen "purely natural" black flowers in nature... Why is this? Why are there so few black flowers in nature?
Regarding this issue, people have proposed two hypotheses.
01
Hypothesis 1:
Flowers are also afraid of " sunburn "
I wonder if you have noticed that when we walk under the scorching sun in black clothes, it always feels hotter than wearing white clothes. This is because black objects absorb almost all natural light (such as ultraviolet, visible light and infrared rays ), and the absorbed infrared rays often increase the temperature of black objects, thus becoming hot.
People who hold the first hypothesis believe that the reason why black flowers are lacking in nature is because black flowers will also absorb almost all the color light from the sun, causing themselves to heat up quickly, and then burn, and then apoptosis. Let's call this hypothesis the "burn" hypothesis.
The "burn" hypothesis explains the "black flower" problem from a physical perspective. Although there are some reasons, some people have raised questions.
Questioners believe that if black flowers are really “burned” and there are no black flowers in nature, then why are black flowers rarely seen in the shaded areas with little sunshine? Without the threat of sunshine, there should be a large number of black flowers in the tree-shaded area.
And the fact is that except for some purple to black buds of Astronaga , there are no other typical black flowers in the tree-shaded land.
0 The Buddha Flame Bun of the Japanese Stinky Swine in the Nanxing Family, Image Source: Wikipedia
In addition, with the continuous development of gardening, gardening enthusiasts have cultivated many black flowers, such as the "noble" black flowers I saw when visiting a flower shop. They are also cultivated in the sun, but they are not burned by the sunlight.
From this we can see that the "burn" hypothesis is not considered very comprehensively. Next, let’s take a look at the second hypothesis.
02
Hypothesis 2:
Flowers' "good friend"
The perspective of the second hypothesis is different from the first one. Supporters look at the "black flowers" problem from the perspective of species evolution.
Since plants cannot move freely, they need to use flowers to attract various animals to help pollinate themselves, such as bees. The second hypothesis is that bees may be the answer to the question of "why are black flowers missing in nature?" We can call it the "bee" hypothesis.
As the backbone of animal pollination, bees and flowers have a very far-reaching relationship.
If we go back to 130 million years ago, we will find that it was the time when the flowering plant began to emerge on the earth, and it was also a period of evolution of bees. For 130 million years, black flowers have not accumulated a lot in nature, which may be inseparable from the choices made by bees as pollinators for flowers.
For organisms in nature, their evolution is completely random. Organisms may evolve into various shapes, colors and structures. However, only organisms that adapt to the natural environment can survive through natural selection. And the important pollinator, bees, whose preferences are a choice pressure for plants.
So, how do bees choose flowers? Why do they ignore black? Is it because they have a more colorful world?
As for the question of whether bees can see a colorful world, Austrian animal behaviorist Carl von Frich got the answer through experiments as early as 1914: bees have colorful vision, and the world in their eyes is indeed colorful.Frich's experiment operation is not complicated. The steps are as follows:
Frich first coats the blue paper sheets with honey, so that the bees "know" that the blue paper sheets can provide honey, thereby establishing connections with the blue paper sheets, that is, training bees;
Frich then places the blue paper sheets without honey among many gray paper sheets, and the grayscale of these gray paper sheets is different;
Then, the training bees are placed in these paper sheets, allowing them to move freely and observe them. Observation can produce two possible results:
If bees do not have color vision, they will not be able to distinguish blue from gray paper sheets similar to blue grayscale, so the number of bees that fall on blue paper sheets and gray paper sheets that are the same as blue paper sheets;
If bees have color vision, they will only land on blue paper sheets.
After observation, it was found that the experimental results were very obvious. The trained bees only landed on blue paper, proving that the bees have color vision.
Later scholars imitated Frih’s experiment and could see bees landing on blue-colored paper sheets and the color visual range of bees obtained from the experiment. Image source: Reference [1]
Later, scholars tested the vision of bees through electrophysiological technology and found that the visible light wavelength range of bees is between 300 nanometers and 650 nanometers. It was also found that there are three photosensitive cells in the compound eyes of bees, which are most sensitive to light of three wavelengths, namely: ultraviolet light with a wavelength of 335 nanometers, blue light with a wavelength of 435 nanometers and green light with a wavelength of 540 nanometers.
Scholars generally believe that the reason why bees are attracted to flowers is mainly because bees are attracted to ultraviolet rays, and they can see the ultraviolet rays reflected by flowers. In introducing the first hypothesis, we learned that black absorbs almost all light including ultraviolet, visible and infrared rays. In other words, black reflects these lights extremely inefficiently, so black flowers are not so attractive in the eyes of bees. Even if black flowers appear in 130 million years, they will be "ignored" by bees and cannot expect bees to help them pollinate.
But in fact, bees are also attracted by the smell of flowers, so we cannot just assert that bees will not pollinate black flowers from the perspective of color.
03
Which is right and wrong
Although the two hypotheses have their own reasons, there are some things that are not considered thoroughly. More and more in-depth research is needed on the issue of "Why nature lacks black flowers". Although the hypothesis is not complete, proposing hypothesis can at least allow us to think about the problems we encounter from more perspectives.
Finally, when discussing the "burn" hypothesis, we mentioned one of the few flowers close to black in nature - the purple to black Buddha flame buds of the Astral family in the woods.
Here I leave you a little thought, guess which insects are pollinated by them? A tip: their scent doesn't seem so pleasant [2].
Arum purpureospathum (Arum purpureospathum) on Crete, Greece Picture source: NicholasTurland
References:
[1] Charles Henry Turner and the cognitive behavior of bees. Martin GIURFA, Anaclara Giurfa de BRITO, Tiziana Giurfa de BRITO, Maria Gabriela de BRITO SANCHEZ
[2] Liu Dexin, Wang Qingfeng, Yang Chunfeng (2022) Flower diversity and pollination strategies of Aristoclasaceae. Biodiversity, 30, 21426.
Author｜Taoryl
Review｜Wang Kang Professor-level senior engineer, Director of the North Garden Science Museum of the National Botanical Garden; Yao Yuan Associate Researcher at the Institute of Bee Research, Chinese Academy of Agricultural Sciences
(Popular Science China)
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