Bitter Dock
Rumex obtusifolius
Knotweed family (Polygonaceae)

Description: This perennial plant is 2-3' tall. Initially, it consists of a rosette of basal leaves, from which one or more flowering stalks develop. The basal leaves are up to 1' long and 4" across. Their petioles are long and slender, while their blades are oblong-ovate or oblong-cordate, crisped and slightly undulate along the margins, and glabrous. The central vein of each basal leaf is often tinted red, and a reticulated network of fine secondary veins is observable across the upper surface. The leaf base is slightly cordate or well-rounded, rather than tapering or wedge-shaped. The cauline leaves alternate along the flowering stalks. They are similar in appearance to the basal leaves, although somewhat shorter in length and more narrow; their petioles are also shorter. The stalks are round, slightly ribbed, and glabrous; they often have prominent longitudinal veins that are tinted red. Each stalk terminates in a panicle of whorled racemes up to 1' in length. The whorls of greenish red flowers are somewhat interrupted along the length of the racemes. The flowers droop downward from pedicels about " in length when they are fully developed. Each flower is about " long, consisting of 6 sepals (3 inner and 3 outer sepals) and no petals. Like other Rumex spp. (Docks), Bitter Dock is monoecious and has staminate (male) and pistillate (female) flowers on the same plant. Both types of flowers are intermingled together on the racemes. The male flowers have 6 stamens and inner sepals that are dull yellow, while the female flowers have a pistil and inner sepals that are often red. As the female flowers develop, their inner sepals become enlarged and surround a single tubercle (hard-coated seed). Each face of this tripartite fruit is oval-cordate or oval-deltoid in shape; its margins are membranous and there are 2-4 spiny teeth along each margin, particularly in the upper half. In bright sunlight, these fruits often turn bright red and are rather colorful. The blooming period usually occurs during the late spring and lasts about 2 weeks, after which the fruits mature slowly during the first half of the summer. The flowers are wind-pollinated and there is no floral scent. The hard-coated seeds are ovoid-oblongoid and rather large in size. Surrounded by the membranous inner sepals, they can float on water or blow about in the wind. The root system consists of a stout taproot. This plant spreads by reseeding itself.

Cultivation: The preference is full or partial sun, moist to mesic conditions, and a loamy fertile soil. This robust plant will grow readily in less favorable situations, but it will be smaller in size. It can tolerate temporary flooding and is more often in partially shaded situations than many other Rumex spp. (Docks). The seeds of Docks can persist in the ground for several decades and remain viable.

Range & Habitat: The non-native Bitter Dock is a fairly common plant that occurs in the majority of counties in Illinois; it is least common in the NW and north central areas of the state (see Distribution Map). Habitats include moist woodland edges, seeps, semi-shaded areas along streams, gardens and edges of yards, areas along buildings, vacant lots, roadside ditches, and waste areas. Bitter Dock is native to Eurasia and prefers disturbed areas.

Faunal Associations: Because the flowers are wind-pollinated, they attract few pollinating insects. Sometimes beetles and other insects lurk in the dense whorls of flowers and fruits. The foliage of Docks is eaten by the caterpillars of Copper butterflies, including Lycaena hyllus (Bronze Copper) and Lycaena helloides (Purplish Copper). The caterpillars of some moths also eat the foliage of Docks, including Phragmatobia fuliginosa (Ruby Tiger Moth), Sunira bicolorago (Bicolored Sallow), and Phlogophora iris (Olive Angle Shades). The caterpillars of the moth Luperina passer (Rustic Dock) feed on the roots. Various birds eat the seeds of Docks, including the Greater Prairie Chicken, Bobwhite, Redwing Blackbird, Bobolink, Swamp Sparrow, and Song Sparrow. The seeds of Docks are also eaten by some sparrows during the winter, including the Vesper Sparrow, Fox Sparrow, and White-Crowned Sparrow. Ducks occasionally eat the seeds of plants occurring in wetland areas. Mammalian herbivores usually shun the foliage of mature plants because it is bitter and slightly toxic (containing oxalates and nitrates). When livestock are fed the flowering stalks of dock, the seeds can pass through their digestive tracts and remain viable. Thus, these animals can help to spread the seeds into new areas.

Photographic Location: The plants in the photographs occurred in a vacant lot and along a roadside in Urbana, Illinois.

Comments: Bitter Dock is one of the more ornamental species of Docks. It is fairly easy to distinguish from other Docks by its shiny leaves, which are rather broad, well-rounded or cordate at the base, and crisped along their margins. Another distinctive characteristic is the appearance of the calyx, which has spiny teeth along its margins. Another common name for this species is Broad-Leaved Dock.

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