Knotweed family (Polygonaceae)
Description: This adventive perennial plant is 1–3' tall and little branched, except where the flowers occur. Initially, it consists of a rosette of basal leaves about 1' across. A flowering stalk bolts from this rosette during the late spring. This stalk is round in cirumference, hairless, and ribbed. The alternate cauline leaves are up to 6" long and 1" across (excluding their petioles). They are oblong-lanceolate, hairless, and dull green. Their margins are crisped and undulate up and down. Their petioles are up to 2" long, becoming broader at the base. The basal leaves have a similar appearance, except that they are somewhat larger in size, their petioles are longer, and their margins are less crisped or wavy. The inflorescence consists of a panicle of racemes with whorls of flowers; it is about ½–1½' long. Each plant has perfect (bisexual) and pistillate (female) flowers; they are pollinated by the wind.
Each yellowish or reddish green flower is about 1/8" long and consists of 3 inner sepals, 3 outer sepals, 3 styles, and an ovary. Perfect flowers also have 6 stamens. There are no petals. Each flower has a drooping pedicel about ¼" in length. The blooming period occurs during the summer and lasts about a month. There is no floral scent. Each flower matures into a dry fruit about 1/6" long that contains a single seed. The inner sepals become larger in size and membranous (at this stage, they are often called 'valves'). Each membranous sepal is cordate-oval in shape and only slightly indented or well-rounded at the base. There is an elongated tubercule that is about 1/3–1/2 the length of the sepal. The margin of each sepal can be smooth or irregularly undulate, but it lacks conspicuous teeth of any kind. The fruit and stems of Curly Dock become dark brown with maturity. The rather large seeds are dark brown and 3-angled, tapering at their tips. They are distributed to some extent by wind or water while adhering to the membranous wings of the fruit. The root system consists of a stout taproot that has a pale yellow interior. This plant spread by reseeding itself.
Cultivation: Curly Dock occurs at sites with full sun, moist to dry conditions, and soil containing loam, clay-loam, or gravelly material. It withstands drought, temporary flooding, and occasional mowing. The seeds can persist in the ground for several decades (at least 50 years) and remain viable.
Range & Habitat: Curly Dock is a common plant that probably occurs in every county of Illinois (see Distribution Map). It is native to Eurasia and was first observed in the United States during the 18th century. Habitats include seeps, glades, weedy meadows (including areas prone to occasional flooding), pastures and fallow fields, vacant lots, roadside banks and gravelly areas along railroads, edges of yards and gardens, and miscellaneous waste areas. Disturbed areas are preferred.
Faunal Associations: Few insects visit the flowers because they are wind-pollinated. The foliage and other parts of Rumex spp. (Docks) are eaten by the caterpillars of Lycaena spp. (Copper Butterflies) and various species of moths (see Moth Table). In particular, the caterpillars of Lycaena phlaeas americana (American Copper) occasionally feed on the foliage of Curly Dock, although they prefer Rumex acetosella (Sheep Sorrel). Various upland gamebirds and granivorous songbirds eat the seeds of Docks, particularly during the winter (see Bird Table). Meadow Voles eat the foliage, while White-Footed Mice eat the seeds. Other mammalian herbivores, however, tend to shun the foliage of Docks because of its bitter taste and mild toxicity. The foliage can be high in nitrates and oxalates.
Photograph Location: A vacant lot in Urbana, Illinois.
Comments: Curly Dock is the most common and weediest Dock in Illinois. This species adapts to dry areas with poor soil surprisingly well, although it also occurs in degraded wetlands. Like other Docks, it is rather tall-growing and long-lived, unless subjected to excessive disturbance. Curly Dock can be distinguished from other Rumex spp. (Docks) in Illinois by considering the following attributes: 1) Its leaves have margins that are crisped and curl up and down, 2) the upper surface of its leaves is usually dull, rather than shiny, 3) each membranous sepal of the dry fruit has an elongated tubercle (for a total of 3), 4) the margin of each membranous sepal lacks conspicuous teeth, and 5) each membranous sepal is cordate-oval in shape and only slightly indented or well-rounded at the base. Other Docks tend to have leaves that are more shiny and flattened along the margins, and the membranous sepals of their fruits are shaped differently. Furthermore, some Dock species have only a single tubercle per fruit. A tubercle is an ovoid swelling near the base of a membranous sepal; it should not be confused with the seed at the center of the fruit.