Classed on the National Invasive Species Database as ‘High Impact Invasive’ with the greatest number of records in the north-east, this is a handsome, hairless, aquatic perennial that is a popular ornamental pond plant. It was introduced into Ireland in the 19th century and was subsequently found in several lakes and other water bodies, mainly in the northern half of the country. It favours still and slow-flowing water where it bears attractive yellow, 5-petalled flowers (3-4cm) in small clusters on stalks which rise from the surface of the water from June to September. The petals are fringed and slightly turned-in. In a similar manner to the flowers of Primroses, Cowslips and Bog-bean, some of these flowers may be ‘pin-eye’ and others ‘thrum-eye’ (see Primrose page for explanation). This is a bottom-rooted species which has meter-long stolons which lie below the surface of the water. The floating leaves are circular to heart-shaped, 3-10cm long. The fruit is a capsule which contains flat, oval seeds which have hairy edges. While it resembles the Yellow Water-lily, it is not a member of the Water-lily family, instead belonging to the Bogbean or Menyanthaceae family.
I first saw this species in 2014 at Ballycroy in County Mayo where I photographed it. The flowers were at the far side of a large pond so the images are not brilliant – maybe another time I might get a better picture.
If you are satisfied you have correctly identified this plant, please submit your sighting to the National Biodiversity Data Centre