Flower:

Branching clusters at the top of the plant, each branch with numerous whorls of 20 to 25 slender-stalked flowers, usually crowded towards the branch tips and more widely separated below. Flowers are less than ¼ inch long (3.5 to 5 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.

The 3 inner tepals, also called valves, are egg-shaped to nearly round, about as wide as long at maturity, distinctly veined across the surface, the edges mostly flat with 4 to 10 sharply pointed teeth per side. At the base of each inner tepal is a projection called a grain, about half as long as the tepal, narrowly egg-shaped with a blunt or rounded tip, the grains of all 3 tepals about the same size. 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 longer than the inner tepals at flowering time, with a distinct, swollen joint in the lower third.

Leaves and stems:

Leaves are both basal and alternate, hairless though sometimes rough along the veins on the underside, toothless to scalloped around the edge and crinkly-wavy though sometimes weakly so, sharply pointed at the tip, the base wedge-shaped to straight across. Basal leaves are lance-oblong, 6 to 10 inches long and to 2½ inches wide, on a stalk shorter than 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, dark brown or reddish brown, and 2 to 2.5 mm long.

Notes:

Narrowleaf Dock is an uncommon weed of moist, disturbed soils and 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. Narrowleaf Dock has crinkly-wavy leaves, tepals up to 5 mm long that are distinctly toothed around the edge, 3 grains of about equal size, grains half as long or less as the tepal, and the flower stalk with a swollen joint in the lower third. It has one of the smallest tepals of the Minnesota docks.

Of the other docks with crinkled-wavy leaves, the most common by far is Curly Dock (Rumex crispus), which is like Narrowleaf Dock in all respects except it has toothless tepals and the 3 grains are not equal in size. Likewise, Field Dock (Rumex pseudonatronatus) is similar in all respects except its tepals are toothless and essentially grainless as well. The only other dock in MN with distinctly toothed tepals is Bitter Dock (Rumex obtusifolius), which has broad, heart-shaped basal leaves and the 3 grains are not equal in size.

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