I am aware that this question has been asked before on the members' forum, but that has now expired. We now know that Lobelia fatiscens is the entity previously described as the native 'Isotoma fluviatilis'.
However, it would be useful to know the actual name of the entity that is being sold by some nurseries as Isotoma fluviatilis, as Isotoma fluviatilis is not listed as an exotic species on the website. Is it a form of Lobelia pedunculata or somthing else ? If people know exactly what it is, they can be discouraged from cultivating the exotic plant, when thinking they are buying a native.