Najas guadalupensis

Southern Naiad

NATIVE TO MAINE OR INVASIVE? STATUS UNCERTAIN

Habitat: Southern naiad is found in the submersed plant community, inhabiting ponds and steams and occasionally brackish waters. This species seems to be more tolerant of warm water temperatures, turbidity and eutrophication than other Najas species.

Description: The slender stems of southern naiad are typically long (up to 1 meter) and wispy. Leaf arrangement on a single plant may be variable, generally opposite, or sub-opposite, but sometimes in whorls, or in crowded clumps along the stems. The leaves are 1 – 2 cm long, strap-shaped and rather blunt at the tip (by comparison, the leaves of slender naiad are quite pointed at the tip). Smaller leaves may occur in the axils. The teeth (actually fine spines) that occur along the margin are so minute they may even be hard to see with a good hand lens. This helps to distinguish this plant from the invasive naiad on Maine’s watch list: European naiad. The serrations on the leaves of European naiad are generally visible without magnification. A second characteristic that distinguishes southern naiad from its invasive counterpart is the leaf base. Southern naiad leaves broaden gently where they meet the stem (like sloping shoulders), unlike European naiad with its squarely bulging, fringed leaf-bases. (You may need to carefully pull the leaf away from the stem to see the base.) The tiny, inconspicuous flowers, followed by slender fruits, develop in the leaf axils. The fruits ripen brown to purple and have 10 to 20 rows of tiny pits along the surface, visible under hand lens.

Origin and Range: The range of this plant in the US is widespread but spotty, with most occurrences east of the Rockies. Southern naiad is native to some parts of New England, but it is not certain if Maine is part of this plant’s native range. Najas guadalupensis is currently known to occur in only one Maine waterbody. (There is a historical record of a second waterbody of occurrence, but no “voucher” specimen on file to back up the record.)

Southern naiad is considered as an invasive species by several other New England states. The Maine Natural Area Program recommends that this species be monitored for its potential to be a nuisance in Maine. Of the three Najas species occurring in Maine (slender naiad, southern naiad and thread-like naiad) slender naiad (N. flexilis) is most common by far.

Annual Cycle: Unlike most aquatic plants, southern naiad is a true annual, dying back completely in the fall and relying upon seeds to return in the spring. Vegetative reproduction may occur during the growing season. Tiny flowers occur in the leaf axils through midsummer and seeds occur by mid to late summer.

Value to the Aquatic Community: The stems, leaves and seeds of southern naiad provide food to waterfowl and different marsh birds and muskrats. The branches offer food and habitat for many fish and invertebrate species

Look Alikes: European naiad, thread-like naiad, and slender naiad. Southern naiad may be confused with some of the small form, fine-leaved pondweeds.