Rumex obtusifolius (Bitter Dock)

Plant Info
Also known as: Broad-leaved Dock
Genus:Rumex
Family:Polygonaceae (Buckwheat)
Life cycle:perennial
Origin:Europe
Status:
  • Weedy
Habitat:part shade, sun; moist, disturbed soils; shores, floodplains, woodland edges, roadsides, fields
Bloom season:June - July
Plant height:2 to 4 feet
Wetland Indicator Status:GP: FACW MW: FACW NCNE: FAC
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: 3-petals Flower shape: indistinct Cluster type: panicle Cluster type: whorled

[photo of flower clusters] Branching clusters at the top of the plant, each branch with numerous whorls of 10 to 25 slender-stalked flowers, the whorls not usually crowded on a branch. Flowers are up to about 1/4 inch long (3 to 6 mm), light green to pinkish, 3-sided with 2 series of tepals (petals and similar sepals) and the outer tepals much smaller than the inner.

[photo of flowers] The 3 inner tepals, also called valves, are triangular to egg-shaped, usually blunt at the tip, distinctly veined across the surface, the edges mostly flat with 2 to 5 large teeth per side that develop with maturity. At the base of at least one inner tepal is a projection called a grain, up to half as long as the tepal, narrowly egg-shaped with a rounded tip, typically 1 grain per flower but sometimes 3 with 2 grains smaller or with only somewhat swollen midveins. Tepals are spreading at flowering time, revealing stamens and styles, and close up after pollination. Flower stalks are very slender and smooth, shorter than to a little longer than the inner tepals at flowering time, with a distinct, swollen joint in the lower third, sometimes near the middle.

Leaves and stems: Leaf attachment: alternate Leaf attachment: basal Leaf type: simple

[photo of basal leaves] Leaves are both basal and alternate, hairless though sometimes rough along the veins on the underside, toothless to coarsely scalloped around the edge, rounded to softly pointed at the tip, the bases rounded to distinctly heart-shaped. Basal leaves are up to 10 inches long and to 5 inches wide, oblong to egg-shaped, on a stalk about as long as the blade. Edges are flat to slightly crinkly-wavy.

[photo of upper stem leaves] Leaves become more narrowly lance-oblong and shorter stalked as they ascend the stem. At the base of the leaf stalk is a brownish papery sheath (ocrea) that surrounds the stem and mostly disintegrates with maturity. Stems are stout, erect, single or multiple from the base, mostly unbranched except in the flower clusters, ribbed and hairless though may be rough along the ridges.

Fruit: Fruit type: capsule/pod Fruit type: seed without plume

[photo of mature fruit] A flower produces a single seed, wrapped in the persistent tepals, which form a capsule-like structure and dry to rusty brown.

[photo of grain variations, and seed] Seeds are 3-sided, egg to teardrop-shaped tapering at the tip, brown to reddish brown, and 2 to 2.7 mm long.

Notes:

Bitter Dock is an uncommon weed of moist, disturbed soils but is likely under-reported in Minnesota. There are at least 11 similar Rumex species in the state, 5 of which are native. Some of the distinguishing characteristics are whether the leaves are crinkly-wavy or relatively flat, the shape of the inner tepals at maturity, size and shape of the grains, whether the grains on all 3 inner tepals are about the same size, sometimes the length of the flower stalk, or where the stalk is jointed, or the vein pattern on the leaves. Bitter Dock has crinkly-wavy leaves though may be weakly so, the basal leaves are relatively broad and usually heart-shaped at the base, tepals are up to 6 mm long and triangular to egg-shaped with a few large teeth around the edge, usually with a single grain per flower (sometimes 3 with 1 larger), and the flower stalk has a swollen joint in the lower third, sometimes the middle. Note that immature flowers may not have developed teeth yet, but the broad, heart-shaped leaves should be distinctive. The combination of these two characteristics separate this dock from all others.

We suspect some of the non-native docks, including Bitter Dock, are under-reported in the state, largely ignored because they're all assumed to be the ubiquitous Curly Dock (Rumex crispus).

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More photos

Photos courtesy Peter M. Dziuk taken in Winona County and in Wisconsin.

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