It's a serious fungal disorder referred to as 'white smut '. It's becoming more common in recent years. Sadly, removing the plants might be your only recourse at this point.

The fungus is one of several Entyloma species. You could cut all of the plants to the ground, rake away all of the mulch from the area, hunt up a fungicide to begin treating the new leaves as they grow and MAYBE be able to protect the new leaves. White smut cannot be 'cured'
from infected foliage.

I haven't done any research on this in a couple of years....so dig around a little. Maybe there have been some new developments.