I had to repot one of my Calatheas, because this one was a bit unhappy with the potting configuration.

It has been growing in semi hydro for half a year now, and has been in soil before when I bought it.
This is why the upper parts of the roots are brown-ish.

They make rhizomes, similar to ginger or potatoes, to store energy for the future. From those bulbs can also emerge new shoots if they are near enough the surface, and can be divided there for propagation if the plant is big enough.