Is Snowberry's fruit white from pigment or structural color?

 

The hero of today's postcard is the snowberry (Symphoricarpos Dill. ex Juss.), a member of the family. Honeysuckle family (Caprifoliaceae). The genus name is derived from the ancient Greek words συμφορεῖν (sampforhein), meaning "to bear together", and καρπός (karpos), meaning "fruit". In fact, the fruits on the branches form tightly packed clusters. 

The white fruits on its branches are very conspicuous and decorate parks throughout the winter. The snowberry is native to North America, where it grows in mixed forests and its fruits are eaten by quail, pheasants and grouse. In Europe birds usually do not eat them, although it is noted that European greenfinches and bullfinches sometimes eat snowberry seeds. In any case, not too eagerly, as the berries are preserved on the bush until spring.

The berries are poisonous and contain isoquinoline alkaloids. This is a very broad class of alkaloids, each subgroup of alkaloids of this class is characterized by its action on the body of mammals.

The white color of the fruit is not caused by a pigment. There is only one known white pigment - betulin, which is found only in the bark of birch (Betula sp.), but is absent from snowberry and other plants. So how is it that snowberry fruits are white, and so are the snow-white petals of many plants? It turns out that the air is to blame. In the fruit of the snowberry and in the white petals of the flowers, there is a lot of empty space between the cells that is filled with air, and in the cells themselves there are no pigments, molecules of substances that absorb light of a certain wavelength. The sun's rays that pass through the snowberry fruit in an unaltered form are repeatedly reflected from the cell walls, and that is why we see them as bright white.

Using a binocular, you can see the air cavities inside the snowberry fruit that give the soft tissue a spongy structure. Inside the fruit are the seeds of the snowberry. In the photo you can also see two deep cavities where the seeds are located.

At the moment, 16 species of Snowberry are known. However, not all species have white fruits. There are species and hybrids in which anthocyanins accumulate in the skin of the fruit and they have a pink color, they are called pink snowberry (Symphoricarpos microphyllus), there is a species with purple-red fruits (Symphoricarpos orbiculatus), called coralberry, and one species (Symphoricarpos sinensis Rehder) - blue-black with white plaque fruits. This species, unlike the other 15, is native to China. This species, unlike most North American species, is not frost hardy, so it is not used to decorate parks in the temperate zone.

References:

Jones, George Neville 1940. A monograph of the genus Symphoricarpos. Journal of the Arnold Arboretum 21(2): 201-252.