This is a perennial (ht to 1.2m) related to the evening primrose plant (Oenothera inthe Onagraceae family of plants. Its tendency to self-seed has led it to be banned from sale in nurseries for a few years. Those of us who bought it before this ban will never be without it in our gardens becuase of its self-seeding ways - and I still like it very much for its graceful wands of wiry stems, bearing white or pink butterfly-like blooms. They are good plants for growing at the front of a border to provide a sort of see-through screen to plants behind. Its origins are in Louisiana and Texas in Northern America, so it enjoys our summer heat. It is best in full sun and needs no special soil. If cut back back half after its first flush of bloom in spring and early summer and given a dose of fertiliser, it will rebloom till autumn. It should be cut back to its woody base in winter.