Those are Maranta leuconora, which are supposed to be very hard to grow from what I've heard.
The mother plant also grew this fast, so I made a few cuttings to propagate her.
That's how she looks now:
I can't stop them from flowering...
The only issue so far has been that I've simultaneously both over-fertilized AND let them run dry while having extremely low air humidity. Like extremely low. This resulted in all existing tips burning, but this hasn't happened yet again on the new growth and hopefully never will.
