Persicaria lapathifolia

Native

Common

Wet to moist. Lake shores, pond edges, marshes, wet prairies, ditches, railroads, roadsides, gravel bars, disturbed sites. Full to partial sun.

July to September

Greenish-white

24″ to 60″

This is a 24″ to 60″ tall, erect, annual forb that rises from a taproot and shallow, fibrous roots.

The stems are ascending to erect, occasionally branched, round, and hairless. They are conspicuously swollen at the leaf nodes.The Latin word polygonum is derived from Greek and means "many knees or joints", referring to the swollen nodes.

The leaves are alternate, variable in shape but usually lance-shaped, 1½″ to 4¾″ long, and 3 ⁄16″ to 1½″ wide. They are on leaf stalks up to ⅝″ long. The leaf stalks wrap around the stem with a membranous sheath (ocrea) at the base. The ocrea is hairless and does not have a fringe of hairs or bristles on the margin. It turns brown as the leaf matures and eventually peels away. The leaf blades are tapered or wedge-shaped at the base and taper to a point at the tip with concave sides along the tip. The upper surface is hairless. The lower surface is usually hairless, sometimes covered with short, soft, woolly hairs, especially when young. The margins are untoothed. There is sometimes a dark blotch in the middle of the leaf blade, but it is neither as common nor as prominent as with spotted lady’s thumb (Persicaria maculosa).

The inflorescence is an unbranched, spike-like cluster (raceme) at the end of the stem and branches and sometimes also rising from the upper leaf axils. The racemes are arching or nodding, dense, 1¼″ to 3⅛″ long, and 3 ⁄16″ to ½″ wide. They are usually not interrupted. The flowers are arranged in several bundles (fascicles) with 4 to 14 flowers each. The fascicles are sheathed at the base and the sheaths overlap.

Individual flowers are 1 ⁄16″ to ⅛″ long. There are 5 sepals and no petals (5 tepals). The tepals are fused at the base. The outer 2 or 3 tepals are egg-shaped to elliptic, usually greenish-white, sometimes pink, with prominent, anchor-shaped veins. There are 5 or 6 stamens and 2 or 3 styles. The stamens have pink or red anthers. The styles are fused at the base. The flowers rarely open, so the stamens, styles, and inner tepals are difficult to see. There is no fragrance.

The fruit is dark brown to black, oval, 1 ⁄16″ to ⅛″ wide achene. The achene is flattened or concave on both sides.

Pennsylvania smartweed (Polygonum pensylvanicum) racemes are mostly held erect, rarely nodding. The flowers are often pink.

Spotted lady’s thumb (Persicaria maculosa) is a smaller plant, no more than 32″ in height. The ocrea has a few short hairs on the margin. There is usually a prominent, dark blotch in the middle of the leaf blade. The flowers are pink to rose.