Here is another herbaceous perennial native to the southern U.S. states and Mexico, Oenothera speciosa, which seems to be well adapted to the mediterranean region. Speciosa means showy, and the pink, rather large flowers are really showy, especially when there are many of them forming a carpet. The stems grow up to 50 cm in height, producing flowers continuously on the upper leaf axils. I got a small clump from somebody in the next village here in Halkidiki some years ago, they have spread very nicely and flower all through the summer. It is drought-resistant and likes full sun; I know it may be invasive, since it spreads by both runners and seeds, but I have not found it to be a problem here, where I am very happy for anything that grows without needing a lot of attention (watering).