Najas gracillima

Thread-like Naiad

NORTHERN NAIAD

NATIVE TO MAINE

Habitat: Thread-like naiad is found in the submersed plant community. It grows in sandy or gravel substrates, usually inhabiting soft-water lakes and ponds. This species is sensitive to pollution and has disappeared in some parts of its natural range.

Description: Thread-like naiad is a delicate plant with slender stems branching lightly near the tips. Leaf arrangement on a single plant may be variable, with leaves occurring in pairs, in whorls, and in crowded clumps along the stems. The very slender, hair-like leaves (1 to 3 cm long and 0.09 to 0.2 mm wide) are very finely toothed along the edges. The teeth (actually fine spines) may even be hard to see with a good hand lens. This helps to distinguish this native 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. Similar to European naiad, thread-like naiad has squarely bulging, fringed (even jagged) lobes at the base of each leaf. The tiny, inconspicuous flowers, followed by slender fruits, develop in the leaf axils. The fruits (about 3mm long) ripen to light brown, with 20 to 45 rows of elongate indentations, or “pits,” along the surface.

The tiny, inconspicuous flowers, followed by slender, smooth-surfaced fruits, develop in the leaf axils. Of the three Najas species occurring in Maine, thread-like naiad (Najas gracillima) is most similar to the listed invasive European naiad (Najas minor). The native can be distinguished from the invader by looking closely at the indentations or “pits” on the surface of the seeds. The pits on the seeds of the native thread-like naiad are longer than wide (elongate along the length of the seed). The pits on the seeds of the invasive European naiad are wider than they are long (elongate around the girth of the seed). Also, later in the growing season, the leaves of European naiad tend to curve backward; those of thread-like naiad do not.

Origin and Range: Thread-like naiad is native to parts of the U.S. and New England including Maine. Its frequency of occurrence in Maine waters is rare. 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, tread-like 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. Flowers bloom through midsummer and seeds occur by mid to late summer.

Value in the Aquatic Community: The stems, leaves and seeds of thread-like 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, and other species of the Najas genus including slender naiad and southern naiad. Thread-like naiad may be confused with some of the small form, fine-leaved pondweeds.