I thought that Ludwigia sp. 'Red' was decided to be a red variety of L. paulustris. Making it Ludwigia paulustris 'Red'. I think it was Chad to was telling me this.
It is very similar in shape so is entirely believeable
palustris seems a bit mroe elongated in leaf form.
i woulnd't mind setting up a comparison grown under the same conditions if i could get my hands on some