Rumex triangulivalvis (Mexican Dock)

Plant Info
Also known as: White Dock, White Willow Dock, Triangular-valved Dock
Family:Polygonaceae (Buckwheat)
Life cycle:perennial
Habitat:part shade, sun; moist sandy or gravelly soil; wet ditches, fields, roadsides, waste areas, brackish or saline shores
Bloom season:June - July
Plant height:12 to 40 inches
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, usually crowded towards the branch tips and may be more widely separated below. Flowers are about 1/8 inch long (2.5 to 3 mm), yellowish-green to greenish-white to pinkish, 3-sided with 2 series of tepals (petals and similar sepals) and the outer tepals much smaller than the inner.

[photo of grains] The 3 inner tepals, also called valves, are mostly triangular, nearly as wide as long, distinctly veined across the surface, the edges flat and slightly jagged. At the base of each inner tepal is a projection called a grain, at least half as long as the tepal at maturity, lance to narrowly egg-shaped typically tapering to a blunt tip, with the grains of the 3 tepals typically all about the same size, sometimes one larger than the others. Tepals are spreading at flowering time, revealing stamens and styles, and close up after pollination. Flower stalks are very slender and smooth, up to 1½ times as long as the inner tepals with a joint in the lower third, often at the base.

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

[photo of leaves] Leaves are all alternate, 2½ to 8 inches long, up to 1½ inches wide (5 to 6 times as long as wide), narrowly lance-elliptic, hairless, toothless, pointed at the tip, tapering at the base, with a faint network of veins and mostly flat blades, the edges sometimes slightly wavy but never crinkled. The lowest leaves are long-stalked, becoming shorter stalked as they ascend the stem.

[photo of ocrea and stem] At the base of the stalk is a brownish papery sheath (ocrea) that surrounds the stem and mostly disintegrates with maturity. Stems are stout, erect, hairless, faintly ribbed, usually branched, and may have a waxy bloom.

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 seeds] Seeds are 3-sided, egg to teardrop-shaped with a short taper at the tip, reddish brown, and 1.7 to 2.2 mm long.


Mexican Dock, formerly known as a variety of both Rumex mexicanus and Rumex salicifolius, is a native species of moist soils found throughout most of 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. Mexican Dock has flat leaves that may be somewhat wavy but never crinkled along the edge, mostly triangular tepals up to 3 mm long, all 3 grains typically about the same, the flower stalk often jointed at the base, and a faint network of lateral leaf veins. Mexican Dock has one of the smallest tepals of the Minnesota docks.

The narrow, flat leaf blades and lack of a rosette of basal leaves distinguish it from all of the Rumex species with more strongly crinkled-wavy leaves, Curly Dock (Rumex crispus) being the most common. The most similar species are Pale Dock (Rumex altissimus) and Swamp Dock (Rumex verticillatus), both of which also have flat leaves. R. altissimus has proportionately broader leaves (2.5 to 4 times as long as wide) and tepals about twice the size, to 6mm long. R. verticillatus has more loosely arranged clusters of long-stalked flowers and tepals up to 5 mm long that are broadly egg to diamond-shaped to 3-lobed and more rounded at the tip. Patience Dock (Rumex patientia) may have relatively flat leaves, but the tepals are more than twice the size (to 8 mm long), round to kidney-shaped, and typically have a single, tiny grain on each flower.

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More photos

Photos by K. Chayka taken in Ramsey County. Photos courtesy Peter M. Dziuk taken in Ramsey County. Photos courtesy John Thayer taken in Itasca County.


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