We are all familiar with the orange `Montbretia` as discarded clumps can be seen in laybys, wasteground and the like. By far the more common is Montbretia itself - Crocosmia x crocosmiiflora, but another, Crocosmia paniculata (`Aunt Eliza`) is increasing and becoming frequent. A third species, Crocosmia masoniorum (`Giant Montbretia`) was found last week at Furnace, Llanelli, perhaps new to Carmarthenshire. The photo shows all three, with (Left to Right), masoniorum first; paniculata in the middle and the familiar Montbretia last. Note that masoniorum are bigger plants with distinctive strongly-ribbed leaves. Also note the different grouping of the flowers with masoniorum and paniculata; the actual individual flowers differ too.
Ed: Ian, for ref, the map below shows how widely naturalised Montbretia now is in West Glamorgan, although Ive only seen 'Aunt Eliza' naturalised at one site. Useful id tips, thanks, Barry.