在特定的物种中旋转的方向是恒定的，例如旋花科植物总是逆时针方向旋转。

The direction of rotation is often constant in a species; for example, Convolvulus always rotates in an anticlockwise direction.

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番薯属是开花植物旋花科中最大的属。

Ipomoea is the largest genus in the flowering plant family Convolvulaceae.

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