I have this growing in my 5.5 gallon in my dorm room and put this stem into my 75 just now. I believe it only has 4 whorls and is a Myriophyllum of some sort.
It came in as a hitchhiker with some R. wallichi, and it wasn't until I noticed that it grew a different color and grew faster that I realized it wasn't just a stem of wallichi acting weird lol.
Any help in the ID of this species would be great
. Probably going to keep it in my 5.5, but not sure if I want it in my 75, or where in my 75 it should ultimately stay.