Which plant type does NOT live submerged in water?

Azolla is a type of floating aquatic fern that typically grows on the surface of water bodies, rather than being submerged. It thrives in shallow waters and can form floating mats, which allows it to absorb sunlight while being buoyant. This floating characteristic differentiates Azolla from the other options listed, which are fully submerged aquatic plants. Vallisneria and Hydrilla are both known to grow underwater, with Vallisneria featuring long, ribbon-like leaves that extend to the surface, and Hydrilla being a highly invasive submerged plant. Spiradelia is also found in water but is usually submerged or partially submerged in aquatic environments. Therefore, Azolla stands out as the only choice that does not live submerged in water.