What describes non-regular geometric shapes found in nature that maintain self-similarity?

The concept being described in the question relates to the idea of shapes that are non-regular but exhibit self-similarity across different scales. Fractals are a class of geometric shapes that fit this description perfectly.

Fractals can be thought of as complex patterns that are built from simple repeating structures, and they are known for their property of self-similarity. This means that if you zoom in on a fractal, you will observe a structure similar to the whole form at different scales. An example of a fractal in nature is the branching of trees, where each branch resembles the overall shape of the tree itself.

In contrast, polygons are regular geometric shapes that have straight edges and do not exhibit self-similarity in the same way. Ellipses are smooth, closed curves that also do not have the characteristic repeating patterns of fractals. Symmetries refer to balanced proportions and can be present in various shapes, but they don't specifically describe the self-similar and intricate nature of fractals.

Therefore, fractals stand out as the correct answer because they are fundamentally defined by their complex, self-similar patterns that can be found throughout nature.