What is a distinguishing feature of floating-leaf pondweed?

Floating-leaf pondweed is characterized by its distinctive oval to heart-shaped floating leaves, which are a crucial identification feature. These leaves float on the surface of the water and can often be seen extending above the waterline, allowing for easy identification when surveying aquatic environments. This morphological trait distinguishes it from other aquatic plants that may have submerged or differently shaped leaves. The shape and floating nature of the leaves are also adaptive features that help in photosynthesis and provide shade for aquatic organisms beneath.

The other options do not accurately describe floating-leaf pondweed. For instance, the presence of only one type of leaf above water is not a feature of this plant since it has leaves that come in various forms including both submerged and floating types. Additionally, floating-leaf pondweed does not grow exclusively in deep water; it can inhabit a range of water depths. Lastly, it is not completely submerged at all times, as its defining characteristic is having a portion of its leaves floating on the surface.