Adiantum

The Adiantum has 200 different species that grows from the Southeastern United States to South America. It  is a species of fern, not one main type. Have you ever seen a fern's roots? A fern's root can be anywhere from 4 inches long and 2 inches wide to  13 inches long and 4 inches  wide. The Adiantum  fern species loves rich soil that grows on the forest's floor. They can be repotted and grown in pots and lasts for year to year as long as the fern's root/seed ball remains alive in good potting soil.

We normally think of a fern as a wispy grass-like plant, but it is not. The system of a fern has a large root that looks like a potato or some kind of root veggie. Adiantum  is a true fern and it's prehistoric like many other plants we don't think about. Ferns happens to be one of the earliest plants that withstood all the prehistoric periods including the ice age.  The Southeastern United States has lots of ferns in it's forests and growing freely in the subterranean climate. It's species thrive in spring to fall and become dormant during the winter months which they are easier to root then.

Sources:

number of species, picure and fern type:
en.wikipedia.org/andiantum

Personal knowledge

You can find more information about the roots and the Adiantum (maidenhair) at:

prairie moon plants and more!