Which native plant can be found floating or along shorelines and has thin, flat leaf blades?

The correct answer is Southern watergrass. This native plant is commonly found floating in aquatic environments or along shorelines, showcasing its adaptation to such habitats. The distinguishing feature of Southern watergrass is its thin, flat leaf blades, which make it easily identifiable in its natural settings. These leaf blades help the plant capture sunlight efficiently, which is crucial for its growth and survival in water.

In contrast, the other options possess characteristics that set them apart. Mosquito fern is a small, floating plant with a different leaf structure; it has feathery, fern-like leaves rather than the thin, flat blades of Southern watergrass. Paragrass has a more robust growth form with broad leaves that do not float naturally. Torpedograss, while it may be found in similar environments, typically has thicker and more rigid leaf blades and is more suited to terrestrial areas compared to the truly aquatic or semi-aquatic nature of Southern watergrass.