This perennial plant is an emergent aquatic that forms clumps of basal
leaves on stout petioles. The ascending basal leaves are 8-24"
long and 4-10" across; they are hastate to sagittate with pointed basal
lobes, smooth along their margins, pinnately veined, medium to dark
glabrous. The stout petioles of the basal leaves are 12-30" long; they
light green and glabrous. The leaves are deciduous in Illinois and
areas, but they are evergreen in areas along the Gulf coast. The tiny
flowers are arranged along a cylindrical spadix that is surrounded by a
narrow spathe; this inflorescence is 4-8" long. The spathe is light
green and glabrous, tapering gradually at both ends; it has
whitish green wavy margins and remains open in the middle. The spadix
is white, cream, or pale yellow. Arrow Arum is monoecious: Fertile
female flowers are located at the bottom of the spadix, while male
flowers are located above. Sterile male flowers are located between
fertile male flowers and fertile female flowers. Each fertile male
flower has 4-5 stamens, while each fertile female flower has a
single-celled ovary with a short style; the flowers have neither petals
nor sepals. The stout peduncle of the inflorescence is 8-18" long,
light green, and glabrous.
The blooming period occurs from late spring
to early summer for about 2-3 weeks. Afterwards, the lower portion of
the spadix develops an ovoid cluster of berries, while rest of the
spadix rots away. As the berries become mature, the peduncle bends
downward, inserting the berries into the water. The tip of the spathe
drills into the underlying muck, releasing some of the berries. The
released berries have the capacity to float on water, thereby
distributing the seeds into new areas. Each globoid berry is about ½"
across; the skin of the berry varies in color from green to brown,
while its interior contains clear mucilage and 1-3 chunky seeds. The
root system consists of stout vertical rootstalks and fleshy fibrous
roots; as the root mass expands, vegetative offsets are formed. This
plant often forms colonies of varying size.
The preference is partial sun to light shade, standing water up to 1'
deep, and muck containing organic matter, sand, or peat. This plant is
bothered by very few disease organisms and insect pests.
Arrow Arum is occasional in southern
Illinois, and the central section of the state along the Illinois
river; it is rare or absent elsewhere (see Distribution
Habitats include swamps, shallow
water along ponds, bottoms of slow-moving shallow rivers, and ditches.
Arrow Arum is typically found in shaded or
partially shaded areas of
wetlands, rather than in open sunny areas.
The unusual inflorescence produces an odor that attracts flies. The
primary pollinator of the flowers is the Chloropid fly, Elachiptera
(Patt et al., 1995). This fly lays its eggs on
tissues of the spadix, and cross-pollinates the flowers while wandering
from inflorescence to inflorescence. The adults feed on pollen. Other
visitors of the flowers include a Syrphid fly, Helophilus sp.
a fruit fly, Drosophila
; the adults of these flies
also feed on pollen. Two semi-aquatic leaf beetles, Donacia
, feed on the foliage of Arrow
Arum (Clark et al., 2004). The berries are eaten by the Wood Duck,
Mallard, and King Rail; these birds probably spread the seeds into new
areas. There is also some evidence that the Snapping Turtle (Chelydra
) and Midwestern Painted Turtle (Chrysemys picta marginata
use Arrow Arum as a food source (Lagler, 1943). Mammalian herbivores
avoid consumption of this plant because of its toxicity: both the roots
and foliage contain crystals of calcium oxalate that can cause severe
irritation of the gastrointestinal tract and kidney failure.
Bottom of a shallow river at the Indiana Dunes
State Park in
NW Indiana, and along a roadside near Cowle's Bog at the Indiana Dunes
National Lakeshore in NW Indiana.
The leaves of Arrow Arum superficially resemble those of another
wetland plant, Sagittaria
(Common Arrowhead). While the
leaves of Arrow Arum have pinnate venation (e.g., a central vein with
lateral veins), the leaves of Common Arrowhead have palmate venation
(even though many of these veins appear to be parallel). Common
Arrowhead also produces a narrow raceme of showy white flowers with 3
petals, which has a very different appearance from the inflorescence of
Arrow Arum. Another common name of Peltandra