I'm not sure if Eric or Anthony had intermingled beds or not. I think they both focused on Thalassia and not the others. I could easily be wrong.

I'd visit them and ask.
Halophila has an intermingling growth, just without Thalassia
What do you mean? Halophila intermingles with Halodule/Syringodium, but not with Thalassia in your tank? Or is that something you've read for field reports? Just curious. The stargrass invades the turtlegrass often in my tanks.
As for benefits, totally unknown to me. I dont know if they can get rootbound in the sense that terrestrial plants (or even freshwater aquatics) do. I dont know if they are limited by substrate resources, or if those potential favorable microbes are then in higher density in older, thicker and intermingled stands of plants.
So many questions.
But the REAL questions here is: is your Halodule sending out new plants
underneath the substrate? And is that H. wrightii, or the Pacific one that Mary sent to you?
The H. wrightii I have only sends out new shoots aerially, it "walks" across the substrate (for lack of a better description). The leading rhizome forms in the water column, along with the new shoot/plant, and is slowly dragged down by roots.
So that's a very interesting observation if they are forming underground for you.
>Sarah