Nuphar submersa is a species of rhizomatous aquatic plant endemic to Japan.
Nuphar submersa is a perennial aquatic herb with slim, branching, prostrate rhizomes. It rarely produced floating leaves. The petiolate, narrowly oblong-triangular, membranous submerged leaves with an undulate margin are 10-18 cm long, and 2-5 cm wide. The petiolate, narrowly ovate floating leaves have a cordate-saggitate base. The petioles are flattened.
The 2-3 cm wide, pedunculated flowers emerge above the water surface. They have five obovate, yellow sepals, which are 1-2 cm long. The 5-7 mm long petals are spatulate. The stamens are recurved after anthesis. The gynoecium consists of many fused carpels. The red, ovoid, 2-3 cm long fruit bears numerous ovoid, 3.5-4.5 mm long, and 2.5-3.5 mm wide seeds.
Nuphar submersa can reproduce clonally.
Flowering occurs from June to October.
It was first described by Takashi Shiga and Yasuro Kadono in 2006.
The type species was collected by T. Shiga at an altitude of 240 m in Koshiro, Imaichi-shi, Tochigi prefecture, Japan on the 29th of September 2004.
Together with Nuphar japonica DC., it forms the natural hybrid Nuphar ÃÂ fluminalis Shiga & Kadono.
The specific epithet submersa, from the Latin submersa, means submerged.
It is critically endangered.
It occurs in rivers and streams.