I think I'm supposed to recognize this, but if so, I've forgotten it. It's at my hotel on Kauai. The trumpet-shaped flowers look like Thunbergia, but they are smaller, maybe 5cm across, no lighter colouring in the centre, and this doesn't seem to be a vine. Oh, wait - I have just queried "purple trumpet-shaped flower angustifolia" and have come up with Ruellia brittoniana, Mexican petunia. Acanthaceae. That's after lots of earlier queries. I was supposed to have learned Ruellia last year, but it was pink. So I guess I don't have a question after all. I'm not sure this colour is accurate enough to decide on a cultivar name.
Looks like Ruellia. Probably Ruellia simplex. Ruellia simplex - Google Search Ruellia simplex - Wikipedia
Thanks for making me really glad I posted this, Silver surfer. Now I understand why it came up when I added "angustifolia" to my search. From your second link: " 'Ruellia simplex C.Wright' is the oldest and accepted name for this species, which has been variously called Ruellia angustifolia (Nees) Lindau, Ruellia brittoniana Leonard, and Cryphiacanthus angustifolius Nees, among several synonyms.[3] The genus is named after French botanist Jean Ruel, while the specific name refers to the simple, not compound leaves".
