Which plant features oval to elliptic leaves that float on the water and has reddish undersides?

The plant characterized by oval to elliptic leaves that float on the water with reddish undersides is watershield. This aquatic plant, scientifically known as Brasenia schreberi, typically has smooth, floating leaves that can give off a reddish tint on their underside. This distinctive feature helps in identifying watershield in aquatic environments.

In contrast, cattail has long, narrow, and strap-like leaves that grow upright rather than floating. Duckweed consists of very small, floating leaf clusters and does not display the oval or elliptic shape characteristic of watershield's leaves. Purple loosestrife features tall, spiky flowers with green leaves but does not have leaves that float on water, further differentiating it from watershield. Each of these plants possesses unique characteristics that clearly set them apart from watershield, making it the correct choice in this case.