This species (Nuphar polysepalum) occurs in ponds and lakes throughout the lowlands of Denali National Park and Preserve. It is perhaps our most visible aquatic plant species – its big, deep green rubbery leaves, and large, bright yellow flowers floating on the surface of ponds are a familiar sight to residents and visitors of interior Alaska’s wetlands. The less visible parts of this amazing plant are perhaps still more memorable. It emerges from the deep layers of organic muck lining the bottom of our muskeg ponds with thick clusters of twining stems that resemble vines rising from a dense tropical forest floor. The stems of this plant can be 5 cm in diameter and two meters long, and are very specialized in order to help the plant thrive in its aquatic habitat. Nuphar and some other groups of aquatic plants have evolved a specialized tissue called aerenchyma, which has up to 8 times the amount of pore spaces within each cell, as compared to terrestrial plant tissues. These large open, balloon-like cells allow large amounts of oxygen and other gasses to be diffused to underwater tissues in order to support cellular respiration and other metabolic work that occurs in below-water plant cells.
Another interesting metabolic adaptation found in Nuphar is anaerobic respiration, which is respiration without oxygen. This process allows the plant to respire using no oxygen in the process, which is a very useful adaptation in the oxygen-poor environment found in standing water such as ponds and lakes. Anaerobic respiration is a complex chemical process that results in the production of ethanol (the same alcohol that you find in mixed drinks) within the plants cells. Ethanol is a poisonous substance in the plant and must be excreted away quickly in order to avoid harm to tissues. One way this toxin is removed is by evaporating the alcohol back up through the balloon-like aerenchyma cells to the surface of the water. One common name for a closely related yellow pond lily in Europe is "brandy-bottle" because of the strong smell of alcohol coming from its flowers (which are at the end of long, tube-like stems filled with aerenchyma tissue). This plant forms large tubers that sprout new clusters of leaves in the spring when ponds and lakes thaw after the long winter. These tubers are storage organs for the sugars that the plant produces each summer – they can be eaten after roasting or boiling, and are quite tasty!
Yellow pond lily occurs across Alaska and in the western half of Canada and the lower 48 United States as far south as Arizona and Baja California. This means that members of this species span the spectrum of aquatic habitats from ponds that remain frozen more than half the year and have mean growing season temperatures of close to 10 degrees Celsius to desert ponds that never freeze and reach extremely warm temperatures for much of the year. This is quite a feat, when you think about it!