Nuphar submersa

Nuphar submersa is a species of rhizomatous aquatic plant endemic to Japan.

Vegetative characteristics
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.

Generative characteristics
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.

Vegetative reproduction
Nuphar submersa can reproduce clonally.

Generative reproduction
Flowering occurs from June to October.

Publication
It was first described by Takashi Shiga and Yasuro Kadono in 2006.

Type specimen
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.

Natural hybridisation
Together with Nuphar japonica DC., it forms the natural hybrid Nuphar × fluminalis Shiga & Kadono.

Etymology
The specific epithet submersa, from the Latin submersa, means submerged.

Conservation
It is critically endangered.

Habitat
It occurs in rivers and streams.