Description: This native annual
plant is about 2½–3½' tall, branching occasionally. The
round stems are hairless and somewhat swollen near the base of the leaves. The
alternate leaves are up to 8" long and 2" across. They are lanceolate, glabrous
or slightly pubescent, and have smooth margins. At the base of each petiole of
the leaves, there is a membraneous sheath (ocrea) that wraps around the stem.
This sheath often has longitudinal ribs, but lacks bristles along its upper
margin. With age, the sheath gradually turns brown and peels away. The upper
stems terminate in spike-like racemes of flowers. These racemes are about 2-8"
long, and droop conspicuously downward. The small flowers are densely crowded
together along the length of the raceme. They are usually white or greenish
white, and less often light pink. Each flower is about 1/8" long, consisting of
5 sepals and no petals. Because the flowers usually don't open fully, the inner
sepals are often difficult to observe. At the base of each flower, there is a
short stout pedicel. The blooming period occurs from mid-summer to early fall,
and lasts about 2 months. There is no noticeable floral scent. Each seed is
dark brown or black, rather flat and oval in shape, and up to 2 mm. across. The
flattened sides of each seed are slightly concave, and they have a shiny
surface. The root system is shallow and fibrous. This plant spreads by
reseeding itself, and often forms colonies.
Cultivation: The preference is full or partial sun,
wet to moist conditions, and fertile soil with abundant organic matter. This
plant is rather weedy, and can be aggressive at disturbed sites. It tolerates
occasional flooding.
Range &
Habitat: Pale Smartweed is a common plant that occurs in most
counties of Illinois (see
Distribution
Map). Apparently, it has not been observed in a few counties in SW
Illinois. Habitats include edges of lakes and ponds, marshes, mudflats and
gravel bars of streams, wet depressions in prairies, ditches along railroads
and roadsides, and moist waste areas. Occasionally, this common plant will
occur at a drier site after a major disturbance, but it will decline in
abundance over time. Pale Smartweed is more common in degraded wetlands than
higher quality sites.
Faunal
Associations: The nectar of the flowers attracts Halictid bees,
wasps, flies, and occasionally small butterflies. The foliage is eaten by
Gastrophysa polygoni (Leaf Beetle sp.), and the caterpillars of the
butterflies Lycaena hyllus (Bronze Copper), Lycaena helloides
(Purple Copper), and Strymon melinus (Gray Hairstreak). The caterpillars
of the latter species eats the flowers and seeds. The caterpillars of several
species of moths also feed on smartweeds (see
Moth Table). The seeds of Pale Smartweed and
other wetland smartweeds are a popular source of food to several species of
ducks, sparrows, and various other birds (see Bird Table). However, because the foliage is
somewhat bitter and peppery, this species is not often eaten by mammalian
herbivores. Overall, the value of this smartweed species to wildlife is quite
high, especially to seed-eating waterfowl.
Photographic
Location: A roadside ditch at the edge of Champaign,
Illinois. This species is locally common in the area.
Comments: This is a large-sized smartweed species.
It can be distinguished from other Persicaria spp. by the lack of
bristles along the upper margin of the leaf sheaths (ocreae), and its drooping
cylindrical racemes, which are densely packed with flowers (usually white).
Other smartweeds have cylindrical racemes of flowers that are held more or less
erect, or they have drooping racemes with flowers that are sparsely distributed
along their length. Pale Smartweed is similar in appearance to another
large-sized smartweed, Persicaria pennsylvanica (Pennsylvania Smartweed)
– however, this latter species has cylindrical racemes that are held more
or less erect, and its flowers are often pink. Another difference is the size
of the seeds: Pale Smartweed has seeds up to 2 mm. across, while Pennsylvania
Smartweed has seeds that are more than 2 mm. across. Another common name for
Pale Smartweed is Heart's Ease, and Polygonum lapathifolium is another
scientific name for this species.