Description: This native perennial plant is up to 4'
tall and unbranched. The stout round stem is light green, and has longitudinal
lines that are darker green. The alternate leaves are up to 10" long and 3"
across. They are lanceolate with
short petioles, and have smooth non-wavy margins.
The leaves are yellowish green or green, and often have a shiny surface. The
entire plant is hairless. At the apex of the plant occurs an erect
inflorescence up to 10" long that branches occasionally. This inflorescence has
dense whorls of small green flowers on drooping pedicels. Each flower is about
1/8" long and has 6 green sepals, sometimes with yellowish or reddish
overtones. The blooming period usually occurs during early summer and lasts
about 3 weeks. If a disturbance lops off the central stem, this plant may bloom
later in the year. There is no floral scent. The blooming period is followed by
the development of numerous tripartite achenes that are initially green, but
later become brown. Each achene is about 1/8" long, has 3 membranous wings, and
a tubercle in its center. When viewed horizontally, any two wings of an achene
form a cordate or orbicular shape with smooth outer margins, while an elongated
tubercle extends more than half-way down the middle of the achene. The
membranous wings provide the achenes within sufficient buoyancy to disperse
them by wind or water. The nutlets can remain viable in the ground for 10
years, if not substantially longer. The root system consists of a long
branching taproot. Colonies of plants are sometimes formed.
Cultivation: The preference is full or partial sun,
and wet to mesic conditons. Growth is best in rich fertile soil, but the
presence of some clay or gravel is tolerated. Established plants can tolerate
some drought.
Range & Habitat:
Pale Dock occurs throughout most of Illinois, and is quite common (see
Distribution
Map). Habitats include moist black soil prairies, clay prairies, prairie
swales, moist meadows around woodlands and streams, thickets, riverbanks, low
areas around lakes and ponds, roadsides ditches, areas along railroads,
pastures, and waste areas. This plant favors moist disturbed
areas.
Faunal Associations: Pale
Dock is wind-pollinated, therefore the flowers attract few insects.
Occasionally, various beetles can be found lurking in or around the
inflorescence.
The caterpillars of some Copper butterflies feed on the foliage of this and
other docks, including Lycaena dione (Gray Copper), Lycaena
hyllus (Bronze Copper), and Lycaena helloides (Purplish Copper). The
caterpillars of some moths feed on Pale Dock, including Lithacodia
carnicola (Pink-Barred Lithacodia), Calothysanis amaturaria
(Crossline Wave; adults often fly during the day), and Luperina passer
(Rustic Dock; larvae feed on roots). It is possible that some birds and small
mammals eat the seeds. Mammalian herbivores, such as rabbits and livestock,
occasionally eat the foliage of young plants, but it is not a preferred food
source. The leaves of mature plants can contain high amounts of nitrates and
oxalic acid. Experimental studies have shown that the seeds remain viable after
passing through the digestive tracts of horses, cattle, sheep, and swine. Thus,
these animals may help to distribute the seeds.
Photographic Location: The upper photograph was
taken at Meadowbrook Park in Urbana, Illinois; the lower photograph was taken
along a railroad in Champaign, Illinois.
Comments: Pale Dock is easily confused with the
Eurasian docks. However, the native docks, as a group, tend to have shinier
leaves with less wavy margins than the Eurasian docks. To identify a specimen
with a specific species, it is necessary to examine the shape and structure of
the mature achenes very carefully. Like other docks, Pale Dock is widely
regarded as an unattractive weed and often destroyed. In general, species of
the Smartweed family suffer from a lack of appreciation by members of the
public (and even professional ecologists). However, Pale Dock is a native plant
that occurs frequently in natural habitats, and it is a potentially important
food source for some insects, as indicated above.