North American Lobelia siphilitica (ht 60 - 90 cm) is an unusual, clump-forming perennial relative of the bedding Lobelia that is grown for spring displays. It is sometimes known as the blue cardinal flower and it blooms in late summer and early autumn with stout spires clustered in the recognisable hooded form of other Lobelia plants, in colours of white or blues. There are other sorts of perennial Lobelia but this is the only one that has steadfastly stayed with me. It self-seeds, especially if there has been a lot of rain, so new plants pop up here and there. It likes a sunny, moist position. Mine sited itself next to Salvia 'Wendy's Wish' and I enjoy the combination of the milky blue Lobelia with the rhubarb colour of the Salvia flowers. I treat it as an annual as it doesn't seem to be perennial in our Sydney climate.