Flower:

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 more widely separated below. Flowers are either male, female, or perfect (both male and female parts), up to about 1/4 inch long (3.5 to 6 mm), yellowish to green to pinkish, 3-sided with 2 series of tepals (petals and similar sepals) and the outer tepals much smaller than the inner.

The 3 inner tepals, also called valves, are mostly egg-shaped to nearly round, distinctly veined across the surface, the edges mostly flat and smooth to slightly jagged. At the base of each inner tepal is a projection called a grain, up to half as long as the tepal, narrowly egg-shaped with a rounded tip, usually all 3 tepals with a grain but 1 or 2 that are less well developed or occasionally absent altogether. Tepals are spreading at flowering time, revealing stamens and styles, and close up after pollination. Flower stalks are very slender and smooth, as long as or a little longer than the inner tepals at flowering time, with a distinct, swollen joint in the lower third.

Leaves and stem:

Leaves are both basal and alternate, hairless, toothless to scalloped around the edge and strongly crinkly-wavy, sharply pointed at the tip, the base wedge-shaped to straight across to nearly heart-shaped. Basal leaves are lance-oblong, up to 12 inches long and to 2½ inches wide, on a stalk nearly as long as the blade.

Leaves become smaller, more lance-linear 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, mostly unbranched except in the flower clusters, ribbed and hairless.

Fruit:

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

Seeds are 3-sided, elliptic to egg-shaped with an abrupt taper to a pointed tip, reddish brown, and 2 to 3 mm long.

Notes:

Curly Dock is a common weed of roadsides, farm fields, an waste areas and was once considered a noxious weed in Minnesota, but Round-up Ready crops took care of that and many other pest plants. While still weedy, it does not create monocultures or invade high-grade habitat. 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. Curly Dock is the most common and best known of the non-native docks in Minnesota, with strongly crinkly-wavy leaves, tepals up to 6 mm long that are egg-shaped to nearly round and only slightly ragged around the edge, usually 3 grains of unequal size (sometimes only 1 or 2), grains half as long or less as the tepal and rounded at the tip, and the flower stalk with a swollen joint in the lower third.

Of the other docks with crinkled-wavy leaves, most similar are Narrowleaf Dock (Rumex stenophyllus) and Field Dock (Rumex pseudonatronatus), both of which are much the same in all respects except R. stenophyllus has distinctly toothed inner tepals and 3 grains all about the same size, and R. pseudonatronatus essentially has no grains at all. Great Water Dock (Rumex britannica), a native wetland species, has larger basal leaves that are more or less flat, 3 grains that are all about the same size and typically taper to a pointed tip. Dooryard Dock (Rumex longifolius) has much broader leaves than Curly Dock, larger, heart-shaped tepals and essentially no grains. Patience Dock (Rumex patientia) has much larger, round to kidney-shaped tepals typically with a single grain less than ¼ the length of the tepal. Bitter Dock (Rumex obtusifolius) has larger, broader, heart-shaped basal leaves and tepals with a few large teeth around the edge.

We suspect some of these other non-native species are under-reported in the state, largely ignored because they're all assumed to be Curly Dock.