I agree, these are the seed pods from a Sweet Gum tree. When a newcomer to the south, I was told these were porcupine eggs. I was not that gullible.
These seed pods broke me from going barefoot in the yard and become wicked missiles when mowing. The trees get doughty in the middle have crashed down when you least expect it. The soft wood doesn't even make good firewood. The only good aspect is the beautiful fall foliage.
I have grown to hate these seed pods but at last can see the value. I don't have much for volunteer weeds in my containers but these should act as a mulch to retain moisture. Thanks for a great idea.