submerged aquatic plant is a summer annual about ¼-1½' long that
branches occasionally. The slender stems are medium green, glabrous,
terete, and flexible; they are about 0.5 mm. across. The leaves occur
at intervals in pairs or pseudo-whorls, often forming dense
aggregations toward the tips of the stems. The leaves are about 1-3
cm. long and 0.1-0.3 mm. across; they are
medium green, narrowly
linear, glabrous, somewhat recurved, and flexible. The leaf margins
have 10-20 teeth on each side that are minute and somewhat bristly (may
require 10x magnification to see). At the leaf bases, there are
individual sheaths about 2-3 mm. long; each sheath is truncate and
bristly-fringed on top. Sessile unisexual flowers develop from the
axils of the leaves (one flower per leaf axil); individual
plants or plant fragments can be dioecious or monoecious. Each
male flower consists of a single stamen, while each female flower
consists of a single pistil. Both types of flower are surrounded by
membranous spathes; they are about 2-3 mm. long. Individual plants can
bloom from mid-summer to early fall. Cross-pollination of the flowers
is accomplished by water currents. The female flowers are replaced by
fruits about 2-3 mm. long that are ellipsoid-oblongoid in shape,
slightly curved, and dark brown or purple at maturity; their tips have
slender beaks. Each fruit contains a single seed that is
ellipsoid-oblongoid in shape. The root system is shallow and fibrous.
This aquatic plant can spread vegetatively by the breakage of its
fragile stems; the resulting plant fragments can drift to new locations
in currents of water. It also spreads by the distribution of its seeds.
The preference is full or partial sun and clear unpolluted water that
is shallow to moderately deep (up to 20' deep). The water should be
relatively low in
nutrients to reduce competition from algae and other plants. Water pH
can vary from mildly acidic to mildly alkaline. The bottom of the water
body can consist of sand or mud. There should be protection from strong
waves and water currents.
Thread-Leaf Naiad is an uncommon plant that is found primarily in
southern Illinois (see Distribution
). It is widely distributed in
NE and north-central United States, Canada, and Eurasia. Populations of
this aquatic plant may be declining because of increased turbidity and
pollution of water. However, because this species is relatively small
and inconspicuous, it may occur in more areas within the state than
current records indicate. Habitats include sheltered inlets
of lakes, ponds, upland sinkholes, and spring-fed pools of water.
Thread-Leaf Naiad is usually found in higher quality wetlands. However,
it is possible to find this species in sheltered ponds near developed
areas if its preference for clear unpolluted water has been satisfied.
In Illinois, this is one of the less aggressive species of Naiad.
Mostly vertebrate animals use the stems,
seeds of Najas spp.
(Naiads) as sources of food. This include several
species of turtles: Chelydra
(Snapping Turtle), Chrysemys
(Painted Turtle), Emys blandingii
(Blanding's Turtle), Pseudemys
(River Cooter), Sternotherus odoratus
(Musk Turtle), and
(Slider). See Lagler (1943) and Ernst et al. (1994)
for more information. Wetland birds also consume these aquatic plants,
especially ducks. Examples of these species include the American Coot,
Mallard, Lesser Scaup, Redhead, and Canada Goose (Havera,
1999; Bellrose, 1942/1978; Martin et al., 1951/1961). For a more
complete list of these species, see the Wetland Bird Table
vertebrate animals that may feed on these plants include muskrats and
carp. Colonies of Naiad plants provide good cover for minnows and other
small aquatic wildlife.
This plant was found in the shallow water
of a pond near Urbana, but it was photographed indoors. A careful
examination of the photos will reveal beaked fruits in some of the leaf
Naiad is a delicate plant with leaves and stems that are
slender and flexible. It superficially resembles other kinds of aquatic
plants, but its leaves have fine bristly teeth along their margins and
its sessile flowers/fruits are produced individually in the axils of
the leaves. Compared to other Najas
(Naiads) within Illinois, Thread-Leaf
Naiad has more slender leaves (only 0.1-0.3 mm. across). A weedy
introduced species, Najas
(Brittle Naiad), is somewhat similar in
appearance (at least earlier in the year), but this latter species has
stems and leaves that are stiff and brittle, rather than flexible.
Both the scientific and common names of plants in this genus (Najas
Naiad) refer to the Water Nymphs, or Naiades, of
ancient mythology. These were lesser female deities who presided
over rivers, brooks, springs, and fountains.