Nuphar polysepalum (USA)

Nuphar polysepalum Engelm. (syn:Castalia polysepala Greene; Nuphar lutea subsp. polysepala (Engelm.) E.O.Beal; Nymphaea polysepala (Engelm.) Greene (ambiguous synonym); Nymphaea polysepala (Engelm.) Kuntze (ambiguous synonym); Nymphozanthus polysepalus (Engelm.) Fern.);   

Alaska, Aleutes, USA (Arizona, California, Colorado, Idaho, Montana, New Mexico,
Nevada, Oregon, Utah, Washington State, Wyoming), Canada (British Columbia,
Northern Territories, Yukon) as per Catalogue of Life;
 

Nuphar polysepala (the yellow pond-lily; syn. Nuphar polysepalum orth. err., Nuphar lutea subsp. polysepala (Engelm.) E.O.Beal) is a species of Nuphar native to western North America.[1][2]  

The name Nuphar is Greek for “water-lily” and polysepala means many sepals.  
It is commonly found in shallow muddy ponds from northern Alaska and Yukon southward to central California and northern New Mexico, and can be recognized easily by its large floating leaves and bright yellow blossoms. 
It reproduces by both seed and rhizome. The rhizomes are underground stems that are thick and fleshy. These rhizomes are hard to pry since they are submerged in mud and are difficult to dig. The leaves float on the water surface, and have an external waxy coating which makes the leaf waterproof and thus allows the leaf stomata to breathe freely; they are glossy green, oval, 10–45 cm long and 7–30 cm wide, with a notch at one side to the leaf stem. The leaves provide shelter for fish. The rhizomes (underground stems) are round and submerged in mud.[1][2] 
The flowers are 5–10 cm diameter, and have 6 to 12 (most often 9) bright yellow petal-like sepals; the true petals are small, hidden near the stamens. Inside the flower from top view anthers can be seen as red and true petals are wedge-shaped and are hidden by the stamens. The fruit is a ovoid green to yellowish capsule 4–6 cm (rarely 9 cm) long 3.5–6 cm wide.[1][2] 
The seeds are edible; they pop like popcorn, and can be steamed as a vegetable, dried and ground for flour, or can be cooked like oatmeal.[2] 
Leaves and rootstocks have been used for ulcerous skin conditions and swelling. The rootstock infusion is used as a traditional gargle for mouth, sore throats and douche for vaginal inflammation. The rootstock is prepared from two tablespoon chopped rhizome with one cup boiling water .[2] 
(From Wikipedia on 30.10.14)

 

 

Nuphar polysepala Engelmann, Trans. Acad. Sci. St. Louis. 2: 282. 1865.
Genus distinct from Nymphaea with pinnate venation of leaves, stigmatic disc without appendages and perianth nearly globose at anthesis, this species has broadly ovate leaves,
Photographed from University of California Botanical garden.