@new240 The plant which Circus identified as anacharis is called elodea in the UK, proper name Egeria densa. (It used to be called Elodea densa but the old name stuck when the proper name was changed)
Floating plants -
Amazon frogbit. This does have one long root per plants and it grows so long it trails on the bottom of the tank. I give mine a haircut just before a water change (so I can hoover up any bits I drop). Also has dense sort roots
Water sprite. This has dense short roots, though the plants themselves grow large. I used to have this but found it difficult to thin out as the 'branches' were all tangled up together.
Water lettuce. I have never had this plant but I think it grows to the same size as frogbit.
Salvinia. Water spangles is Salvinia minima. I had this a few years ago but it turned brown and died one summer. This plant is smaller than the others and doesn't have such bushy roots.
Floating plants -
Amazon frogbit. This does have one long root per plants and it grows so long it trails on the bottom of the tank. I give mine a haircut just before a water change (so I can hoover up any bits I drop). Also has dense sort roots
Water sprite. This has dense short roots, though the plants themselves grow large. I used to have this but found it difficult to thin out as the 'branches' were all tangled up together.
Water lettuce. I have never had this plant but I think it grows to the same size as frogbit.
Salvinia. Water spangles is Salvinia minima. I had this a few years ago but it turned brown and died one summer. This plant is smaller than the others and doesn't have such bushy roots.