Sorosis

Most fruits hang in their own singularity: apples, oranges, and apricots are common examples. Other fruits, such as grapes, form clusters. Still other fruits are formed when a group of flowers merge to create a fruit. Soroses are that type of fruit.

Mulberry fruit (Pikist)

What is fruit?

Fruit is the fertilized ovary of a flowering plant (angiosperm). After pollination and fertilization occur, two new structures are produced: seeds (fertilized ovules) and pericarp (thickened ovary walls). In the case of apples and oranges, one flower produces one fruit. Sometimes, multiple flowers can fuse together to create a fruit. There are three different ways that this can happen:

• syngonium - a large, hollow receptacle holds multiple ovaries on the inside surface [figs]
• coenocarpium - the ovaries, floral parts, and receptacles of many flowers are clustered around a fleshy axis [pineapple]
• sorosis - ovaries of a group of budding flowers merge [mulberry]

In nearly every piece of literature you see, pineapples are listed as a common example of sorosis, but this is incorrect. I don’t know why they do this.

​How a sorosis fruit develops

If you look at a mulberry flower cluster, you will see several flower buds held tightly together. Each of these individual flowers open up, awaiting pollination. 

Clusters of unopened mulberry female flower buds (Fastily) CC BY-SA 3.0

If you look closely, you can see tiny fruits at the base of each flower. Each of these fertilized fruits will develop around the stem that they emerged from in the first place. This is unlike pineapples, which include the receptacles and flower parts in their fruit development.

Close-up of a mulberry flower cluster (JJ Harrison) CC BY-SA 3.0

Berries vs. soroses

While mulberries may appear to have the same structure as blackberries and raspberries, botanically, they are quite different. Raspberries and other members of Rubus are made up of several drupes (a type of fruit) that are clustered around and attached to a dry thalamus. All of the drupes in a single fruit are made from a single flower. In mulberries, and other soroses, each rounded bit is its own fruit, formed from its own flower.

Unripe white mulberry ( Petru Dimitriu) Public Domain

It won’t make any difference, as you enjoy a fig, some pineapple, or a mulberry, but now you can impress your friends with this fascinating word!