I have had floating fern grow into the sponge on my quarantine tanks before. Here, the plants above the sponges are Susswassertang, which attaches, but does not penetrate into the sponge.
On the other side of the tank, I like to use sponges on the output of powerheads to diffuse current a bit. On those, I use Java fern to make it look a bit less industrial. I get a chuckle out of the roots growing in the remaining current...