It`s Najas guadalupensis. It is easy to grow if you like a sort of a floating plant. Shipping can be problematic as it tends to fall apart during transport.
Seeing that the OP @Riley is from S. E. England, one advantage would that Guppy Grass (Najas guadalupensis) grows very well in hard, alkaline water.
It does, Hornwort (Ceratophyllum demersum) <"performs a similar role">, and has similar growth requirements, but it is slightly less prone to dissolving in the post.
Have to admit, I've never seen a display tank use it, but a friend uses it to breed Celestial Danios and Panda catfish - in London tap water - and as the only plant in the tank, it actually looks really attractive. Small tanks, medium intensity warm coloured lighting and very gentle filtration. He does nothing to 'look after' the plant. I keep thinking of an easy hard water tank with Vallis, crypts, guppy grass and hornwort, but I think I am a sucker for hard work. What's not to love about CO2, reducing KH, weekly trimming and having to play about with fertilisers!
Useful to know, somebody told me that they did better in hard water. I'm still considering an unheated hard water tank, but just for Cherry Shrimps and <"fancy snails">.
Panda Cory (Hoplisoma (Corydoras) panda) is the only "hobby bred" "Corydoras" that <"I ever see locally"> and it breeds in our tap water, about 17 dGH and 17 dKH. It is a really smart fish, when its happy, and stays relatively small.
