There are two types of torus in the plant world. One is related to flowers, and the other is a donut-shaped plug that protects plants when they cavitate.
The donut-shaped plug variety occurs within the xylem. The xylem is part of the vascular bundle that pulls water from the ground. The torus found within the xylem protects plants from cavitation. Cavitation occurs when the water pressure within the plant is greater than the atmospheric pressure outside the plant. You can hear it happening to trees in summer. It sounds like a large crack. Cavitation causes sap to vaporize, creating embolisms. The torus, held within a pit called the torus-margo structure, acts as a plug. This plug reduces the spread of the embolism.
Flowering plant torus
The place where a stem meets a flower is called the torus, or receptacle. The torus is the thickened part of a stem from which flowers emerge. Accessory fruits, such as apples and strawberries, grow from the torus. And it is the way you can tell blackberries from raspberries! That mammoth sunflower head? It’s a torus, too.
Types of flowers
The torus is found at, below, or surrounding a plant’s reproductive organs, depending on the species. Flowers can be hypogynous, perigynous, or epigynous. Don’t let the words scare you off. The -gynous part of these words means it refers to the Lady Parts of your plant. Stamens and petals are below the ovaries (or gynoecium) of hypogynous flowers. They are at the same level in perigynous flowers. The ovary is enclosed in the torus of epigynous flowers, with the petals and other parts above. You can use this information to help identify plants and win at Scrabble.
Raspberry or blackberry?
Do you know how to tell blackberries and raspberries apart? It’s not the color. There are black raspberries and red blackberries. The only way to tell the difference between blackberries and raspberries is to look at the way the fruit comes away from the torus.
If the torus comes with the fruit, it is a blackberry. If the torus breaks away from the fruit, it is a raspberry.
Now you know.
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