Polygonum persicaria L.

Lady’s thumb, persicaria, redleg, spotted ladysthumb, Adam’s plaster, lily of the valley

Some similar species

	Polygonum amphibium	Polygonum cespitosum	Polygonum hydropiperoides
Common Name	water smartweed	Oriental lady’s thumb	mild water pepper
Plant	Up to 9½′ (3 m) × ⅜″ (1 cm), sprawling or floating. Ocrea are ⅛–1¾″ (5–50 mm), with the upper part fringed with small hairs 0.5-4.5 mm long.	Up to 3′ (91 cm) in size, sprawling or erect. Ocrea encompassing the joints are long-bristly, and ⅛–⅜″ (4–12 mm) long,, vs. less than ⅛″ (5 mm) for P. persicaria.	6–39″ (15–100 cm) long, but slender and with upper portions usually erect, erect to sprawling. Stems are green to red. (Compare to P. amphibium, with stems up to ⅜″ (1 cm) around, and more often sprawled along the surface of the water). Ocrea are brown, cylindric, and ⅛–⅞″ (5–23 mm) long, with an inflated base, topped with hairs 1/16–⅜″ (2–10 mm).
Leaves	Alternate, and often lanceolate, but they take on many other shapes. They may be floating or upright, with papery sheaths at leaf bases. They are ¾–8″ (2–20 cm) × ⅛–1¾″ (5–50 mm), with petioles 1/32–1″ (1–30 mm). They are not mottled.	Alternate, elliptic to lanceolate, ¾–3″ (2–7.5 cm) × ⅜–1¼″ (1–3.5 cm), and pointed at the base and tip. Petioles are 1/32–⅛″ (1–5 mm). Leaves are not mottled.	Alternate, lanceolate, bristly, with smooth edges. Floating or upright, up to 1¾–6″ (5–15 cm) × ⅜–⅞″ (1–2.5 cm), tapering to a sharp point. Petioles are less than ⅛″ (5 mm) long. Leaves are not mottled.
Flowers	Pink, appearing in a thick oval cluster of tiny five-lobed flowers. The cluster is ¾–6″ (2–15 cm) long. Each individual flower is ⅛–3/16″ (4–5 mm) in diameter. Flowers appear June to September.	Pink/white flower spikes are ¾–1½″ (1.9–3.8 cm) tall × 1/16–3/16″ (3–6 mm) thick, densely filled with individual flowers less than ¼″ (6.3 mm) in size. (By contrast, P. persicaria has flower stalks ⅛–⅜″ (6–12 mm) thick.) Flowers appear from June to October.	Greenish, pinkish, or white flowers form loose, elongated spikes 1–3″ (3–8 cm) long and 1/16–⅛″ (2–5 mm) around. The spikes are on peduncles ⅜–1″ (1–3 cm) long.
Fruit	Tiny brown rounded achenes 1/16–⅛″ (2.5–3 mm) long. Each achene contains one seed. They appear from July to September.	A black achene with a triangular cross section.	Dry, hard, smooth, shiny achenes each contain a single seed. They are 1/32–⅛″ (1.5–3 mm) long, and three-sided.
Range/ Zones
Habitats	Floating in ponds, streams, and marshes	Common to invasive in disturbed habitats such as pastures, roadsides, and lawns. It is partial to wet areas.	Often forming mats along lake or pond margins.

	Polygonum lapathifolium	You are here Polygonum persicaria
Common Name	nodding smartweed	lady’s thumb
Plant	2–5′ (60–152 cm) high, usually upright, some­times sprawling, with green or deep red hairless stems. The ocreas are brownish, tubular, ½–1″ (1.5–3 cm) long, with few or no hairs.	Up to 3′ (91 cm) in height. Stems are openly branched and often reddish. Ocreas have hairs that extend up to 1/16″ (2 mm) from the top.
Leaves	Alternate, typically lanceolate but variable in shape, fatter at the base and tapering to a sharp tip, 1¾–10″ (5–25 cm) × ½–1¾″ (1.5–5 cm). Petioles are ⅜–¾″ (1–2 cm). Leaves have tiny, hooklike hairs that make them feel rough. They are not mottled.	Alternate, lanceolate to elliptic, 1–8″ (2.5–20 cm) long × ¼–2″ (6.3–50 mm) wide. Petioles are ⅛–¼″ (5–8 mm). Leaves often have a dark purplish triangular or lunate patch on them.
Flowers	Greenish-white to pink, in columns about ¼–⅜″ (6.3–9.5 mm) in diameter and 1–3″ (2.5–7.6 cm) long. Numerous clusters may be upright, arched, or drooping. The tiny, individual flowers never actually open.	Tiny pink and white flowers form groups of spikes ½–1½″ (1.3–3.8 cm) long. Flowers appear from June to July.
Fruit	Egg-shaped, less than 1/16″ (2 mm) long, brown to black, glossy, containing a single seed.	Brown to black, glossy, with one seed. They are roughly egg-shaped, but somewhat angular. Each fruit is less than 1/16″ (2 mm) long. Fruits appear from July to September.
Range/ Zones		USDA Zones: 4-8
Habitats	Margins of water bodies, pastures, orchards, irrigated crop fields, and rice fields.	Disturbed soils that are wet or seasonally wet, such as ditches, pastures, grain fields, and water edges.

Polygonum persicaria description by Thomas H. Kent, not updated.

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