The plant that removes the most indoor toxins and releases the most moisture into the air is the Boston Fern or Nephrolepis exaltata “Bostoniensis”.
The Boston Fern is especially good at removing formaldehyde which is a common indoor pollutant.
The Boston Fern is also very good at increasing indoor humidity. It does this by transpiring and releasing moisture into the air.
This is according to B.C. Wolvertonm, the author of How To Grow Fresh Air.
Wolverton originally began his research with the aim of creating a breathable environment for a NASA lunar habitat. What came of that research was the discovery that certain houseplants are the most efficient filters of common pollutants such as ammonia, formaldehyde, and benzene.
The Boston Fern was the top toxin remover out of the fifty Wolverton studied.
A Boston Fern requires some attention. It must have frequent misting and watering or the leaves will grow brown quickly.
See also: Skogluft: Norwegian Secrets for Creating Forest Air in Your Home by Jorn Viumdal