Calystegia purpurata purpurata
Large white flowers. (There are said to be pink and purple variants, but I haven’t seen any locally).
Blooms all year, but is at its peak around May.
May be distinguished from C. macrostegia by the bracts at the base of the flower. In this species the bracts look like tiny little leaves a few millimeters below the flower, while in C. macrostegia the bracts surround, and mostly obscure, the calyx (the sepals at the base of the flower). Also can grow higher up the mountain.