This herbaceous perennial plant forms a small tuft of ascending to
arching basal leaves about 4-12" (10-30 cm.) long. Individual basal
leaves are about 1 mm. across, medium green, terete, and hairless (or
nearly so). One or two erect floral stalks about 8-16" (20-40 cm.) long
develop from the tuft of leaves; these stalks are about 1.5 mm. across,
reddish brown, terete, and hairless. The foliage is reportedly aromatic
when crushed. Each stalk has a narrow raceme of flowers about 3-10"
(7.5-25 cm.) long; these flowers alternate along the stalk and they are
sparsely distributed. Each flower is about 2 mm. across, consisting of
3 purplish green petals, 3 purplish green sepals, 3 fertile green
pistils that are joined together, and 6 inconspicuous stamens. The
outer sepals are orbicular-ovate in shape, while the inner petals have
a flattened-pyriform shape. The stigmas of the pistils are white and
The slender pedicels of the flowers are 2-10 mm.
long, ascending to erect, reddish brown, and hairless. The blooming
period occurs during the summer and early autumn, lasting about 1-2
months for a large colony of plants. The flowers are cross-pollinated
wind. Afterwards, the pistils develop into 3-celled fruits
(schizocarps) about 7-9 mm. long and 1 mm. across. These fruits are
narrowly oblongoid-oblanceoloid in shape and 3-angled; they are
initially green, but later become brown. At maturity, these fruits
divide longitudinally into 3 narrow sections, beginning at the bottom.
The central axis of each fruit is 3-winged; there are 3 seeds per
seeds are similar in appearance to their fruits, but a little shorter
and more slender. The root system consists of a whitish crown with
preference is full sun, wet
conditions, and a barren calcareous soil containing an abundance of
sand or gravel. This plant is intolerant of competition from other
ground vegetation. It is quite cold-hardy.
The native Slender Arrowgrass (Triglochin
palustris) is rare in Illinois, where it is
state-listed as 'endangered.' It is found in the NE section of the
state and 2 counties toward the center of the state (see Distribution
Map). Illinois lies along the southern range-limit of this
the United States, Slender Arrowgrass occurs in the New England region,
Great Lakes area, Northern Plains, and scattered areas of the western
states. It also occurs in Canada, Eurasia, and New Zealand. In
Illinois, habitats consist primarily of fens, calcareous gravelly
seeps, marl flats, and calcareous sandy pannes near Lake Michigan. This
very conservative plant is restricted to high quality natural areas
within the state.
relationships of this plant in Illinois are not known. Further to the
north in Canada and Alaska, the foliage and especially the whitish
crowns are a preferred source of food for the adults and goslings of
several species of geese, including Branta canadensis (Canada
nigricans (Black Brant Goose), and Chen caerulescens
(Lesser Snow Goose). The foliage and crowns of Slender
are reportedly high in protein and low in fiber
(Mulder et al., 1996; Prevett et al., 1985).
The foliage also
contains hydrocyanic compounds that can be toxic to sheep and
cattle if it is consumed in sufficient quantity. There is some evidence
in Europe that the seeds of this plant can cling to the fur of deer and
cattle. Thus, these animals can spread the seeds to new areas (Mouissie
et al., 2005).
A gravelly seep in McHenry County, Illinois.
This plant is not very showy and it is easily overlooked. The only
other species of this genus that occurs in Illinois, Sea Arrowgrass
is also very rare within the state and it occurs
in similar areas. Sea Arrowgrass is a little larger and stouter than
Slender Arrowgrass (Triglochin
palustris) overall. Its fruits
(schizocarps) have a wider ovoid shape and they divide into 6
sections (6 seeds per fruit), rather than 3 sections. Unlike Slender
Arrowgrass, the central axis of its fruit is not winged. The
wind-pollinated flowers of these plants are rather odd-looking because
their feathery stigmas resemble tufts of hair that are typically found
on seeds. An alternative spelling of the scientific name for Slender
Arrowgrass is Triglochin
palustre, and another common name of this
plant is Marsh Arrowgrass.