I only use the leaves from my yard, because I don't use any insecticides or fungicides, but can't be sure about what others do.
I have magnolia, maple, and oak and have used them all.
Maple break down the fastest, of the 3, the longest lasting are the magnolia.
In tanks where I want lots of tannins, I pour boiling water over them and let sit until waterlogged enough not to float. They have worked well as spawning media for killifish, piled up, great places for fry, and the large cichlids rummage thru them and I believe use as part of the diet (especially the detritus feeders.

The leaves do break down, crumble and can make for more maintenance of filters or substrate.

And as someone else said, are always a part of any habitat I have snorkeled in.
Ishot the video below near Tulum in Mexico. Lower the volume so you don't have to listen to my incessant breathing. The fish are Astyanax tetras, Parachromis freidrichthalli, introduced Tilapia, and Gambusia and Poecelia live bearers
Aktun Ha