I did not know that. I would guess the females produce the nuts. We have a bunch of filberts bushes/short trees all around our property. We've planted 4 but the rest are volunteers.Did you know filberts are not self-fertile? You have to have a pollinator to get a crop. I can't remember if the pollinator is male and the nut bearing trees are female, or if it just has to be another species, but remember that we planted one tree in 20 as a pollinator and the rest for nuts.