The Yellow Water-lily is a characteristic sight among the floating leaves near reed beds in backwater sedimentation areas. The species tolerates light currents and, unlike the White Water-lily, regenerates quickly after flooding.
Description
The leaves of the Yellow Water-lily spring from the tip of the plant's creeping, horizontal stem. Rooted in sediment, this stem may be as thick as a human arm. The stem is covered on top with cicatrices and on the bottom with adventitious roots. Numbers of soft, short-stalked submerged leaves are continually formed; they look something like lettuce. For the most part, the leathery floating leaves are able to keep up with rising water levels thanks to the growth of their leaf stalks. The floating leaves are deeply cleft and more pointed than other water-lilies. This characteristic allows differentiation between the Yellow Water-lily and non-flowering White Water-lilies. The yellow flowers of the Nuphar lutea are from 4-6cm in diameter and may be observed from June to September.
Distribution
With a range extending from Europe to Central Asia and even Siberia, the Yellow Water-lily may be found in all Austrian provinces, from lowlands to montane zones. In the Danube wetlands, the species may most often be sighted in the backwaters of the Lobau and on the northern Danube shore.
Endangerment and Conservation Status
Due to its sporadic occurrence in Austria, Nuphar lutea is classified as vulnerable. Its close relative Nuphar pumila is critically endangered: on the one hand, because this Ice Age relict is very rare, and on the other because it forms bastard forms with the Yellow Water-lily. The Yellow Water-lily itself is fully protected in both Vienna and Lower Austria.
Ecological Characteristics
With its fat creeping stem, the Yellow Water-lily grows from the muddy bottoms of waters, including slowly-moving waters, and in depths of up to 4m. It has submerged leaves which are followed later in the year by floating long-stemmed leaves and flowers – unless flooding interferes. In extremely shallow waters, the floating leaves can rise high up over the water's surface. The submerged leaves survive the winter and allow for the continuation of photosynthesis, even under solid ice. The flowers attract pollinators such as flies and beetles not only with their brilliant colour, but also with an intense, alcohol-like aroma. Propagation is on the one hand by way of seeds, which can float and drift for long periods of time, and on the other by the branching out of the creeping stem.
Special Characteristics
Large expanses of floating leaves dominated by the Yellow Water-lily form an important habitat for many types of fish. Much organic material is deposited between the lily stands and thus accelerates sedimentation. In the areas of the wetlands which are subject to flooding, overgrowth of the plant is prevented by occasional flooding.