white evening primrose

O. speciosa is a herbaceous perennial about 30cm high, with creeping rhizomes, basal rosettes of oblong-lance-shaped to lance-shaped mid-green leaves, 2.5-5cm long, which have large triangular teeth or are pinnatifid, arching stems with slightly smaller leaves, and saucer-shaped flowers, up to 8cm across, which open white in the day and become pale pink in the evening, from early summer to early autumn; it is occasionally invasive