Najas guadalupensis is a species of aquatic plant known by the common names southern waternymph,[4] guppy grass, najas grass, and common water nymph.

It is considered native to Canada (from Alberta to Quebec), and most of the contiguous United States, Mexico, Central America, the West Indies and South America.

[5] Najas guadalupensis is an annual, growing submerged in aquatic habitat types such as ponds, ditches, and streams.

It produces a slender, branching stem up to 60 to 90 centimeters in maximum length.

The thin, somewhat transparent, flexible leaves are up to 3 centimeters long and just 1 or 2 millimeters wide.