Pygmy water lily

Nymphaea tetragona (Nymphaeaceae) is a perennial floating-leaved plant and the only water lily native to Japan. It ranges across north-western North America, north-eastern Europe, Siberia, East Asia and northern India; in Japan it grows from Hokkaido to Kyushu in neutral to slightly acidic, nutrient-poor ponds, lakes and ditches. Its Japanese name is usually explained by the flowers opening around the 'hour of the sheep' (about 2 pm). Long stalks rise from a short, thick, unbranched rhizome to oval to elliptic leaves 8–19 cm long, deeply notched at the base and red-purple beneath. From June to September white flowers 3–7 cm across open on the surface, opening and closing for two to three days; afterwards the stalk coils and the fruit ripens under water. The rhizome does not branch, so plants do not multiply vegetatively and are propagated from seed. Smaller than garden hybrids, it is easy to grow in pots and jars. Hybrid garden water lilies are a Priority Control Alien Species in Japan, but this native species is not. Many hybrids have it as a parent, however, so check the scientific name and origin if you want the native species. It is red-listed in many prefectures and already extinct in some, so do not collect it from the wild. It is vulnerable to carp and American crayfish. It is sold by garden centres that handle aquatic plants in Japan.

Source: Wikipedia (CC BY-SA 4.0)

The Pygmy water lily grows to Leaves 8–19 cm long; flowers 3–7 cm across.

A little slow-release fertiliser in the growing season