This submerged aquatic plant is a summer annual about 2-18"
long, although on rare occasions it may become up to 36" long.
Individual plants become more branched as they age. The glabrous stems
are medium green while young, becoming dark green, more stout, and more
brittle with age. Pairs and pseudo-whorls of glabrous leaves about
0.5-3.5 cm. in length occur along these stems, particularly toward
their tips. Young leaves are 0.2-0.5 mm. across, medium green,
and flexible, while older leaves are 0.5-1.2 mm. across, dark green,
stiff, and brittle. The older leaves are usually recurved, creating the
appearance of leafy rosettes at the tips of stems. Along each side of
the leaf margins are 7-15 teeth that are small in size, but
conspicuous. At the leaf bases, there are membranous sheaths about
1.0-2.0 mm. long; each sheath is truncate-fringed along its apex.
Mature plants are usually monoecious, rather than dioecious, producing
sessile unisexual flowers in the axils of their leaves. These flowers
are about 2 mm. long. Individual male (staminate) flowers consist of a
single stamen, while individual female (pistillate) flowers consist of
a single pistil. Both types of flowers are surrounded by a membranous
spathe. The blooming period occurs from mid-summer into the fall. The
female flowers are replaced by beaked fruits that are
ellipsoid-oblongoid in shape, slightly curved, and about 1.5-3.0 mm.
long. Each fruit contains a single seed that is a little shorter than
the fruit. Individual seeds are longitudinally ribbed and faintly
reticulate. The root system is shallow and fibrous. The fragile stems
of older plants are easily broken, creating plant fragments that drift
with their seeds in water currents to new locations.
The preference is full or partial sun, shallow to
moderately deep water (up to 15' deep) that is clear to slightly
turbid, and a water bottom containing sand, silt, or mud. Acceptable
water pH varies from slightly acidic to alkaline. Brittle Naiad is more
tolerant of water that is turbid and polluted than other Najas spp.
(Naiads). It can spread aggressively.
The introduced Brittle Naiad is
common in the southern half of Illinois, while in the northern half of the
state it is uncommon or absent. This plant
has been introduced into eastern North America from Eurasia. In many
areas of North America, it is considered an invasive species. Habitats
include shallow water along lake shores, sheltered lake inlets,
ponds, streams with slow currents, and drainage canals.
Brittle Naiad is especially common in young ponds and other wetlands
that have been created through human agency. It is also found in natural
wetlands that have been degraded by siltation or pollution (e.g.,
fertilizer run-off and other chemicals).
Many species of geese, ducks, and other wetland birds feed on the
foliage and seeds of Naiads (Najas spp.
); see the Wetland Bird
for a list of these species. These aquatic plants are also a food
source for such species of turtles as the Snapping Turtle (Chelydra
), Painted Turtle (Chrysemys picta
), Blanding's Turtle (Emys
), River Cooter (Pseudemys concinna
), Musk Turtle
), and Slider (Trachemys scripta
vertebrate animals that feed on these plants include carp and muskrats.
As an invasive species, Brittle Naiad has been able to spread to new
areas through such human-related activities as: 1) incorrect disposal of
plants in aquariums, 2) transportation of plant fragments and seeds on
fishing nets, and 3) transportation of plant fragments and seeds on
boat trailers, propellers, hulls, and anchors. In addition, it
is likely that the seeds of this plant are transported by
wetland birds to new wetlands on their feathers or muddy feet; perhaps
some of the seeds are also able to pass through the digestive tracts of
these birds and remain viable. Colonies of Naiad plants provide good
cover for minnows and other small aquatic wildlife.
The plant fragments were found in a pond near
Urbana, Illinois, although they were photographed indoors.
Immature plants of Brittle Naiad are difficult
from the uncommon Thread-Leaf Naiad (Najas gracillima
appearance of mature plants for these two species are quite distinct.
Mature plants of Brittle Naiad have leaves that are more wide
(about 0.5-1.2 mm. across), more brittle, and a darker shade of green
than those of Thread-Leaf Naiad; mature plants of Brittle
Naiad also have leaves that are more recurved and their teeth
are more conspicuous. Another species of this genus, Spiny
Naiad (Najas marina
has even wider leaves (up to 2.5 mm. across) than Brittle Naiad and its leaves have teeth that are fewer in
number, but larger in size. So far, Spiny Naiad has been found only in
Lake County, Illinois, where it is probably adventive. Other common
names of Najas minor
include Brittle Water Nymph and European Naiad.