Northern Prairie Wildlife Research Center
Western Wetland Flora
Field Office Guide to Plant Species
Polygonum persicaria L.
- Family: Smartweed (Polygonaceae)
- Flowering: June-November
- Field Marks: This species differs from similar smartweeds by its bristly sheaths, dense, erect spikes of pinkish flowers, and its annual habit.
- Habitat: Moist, disturbed areas.
- Habit: Annual herb with a taproot.
- Stems: Upright or ascending, branched, up to 3 feet tall, usually smooth; sheaths bristly at the tip.
- Leaves: Alternate, simple, lanceolate to linear-lanceolate, up to 5 inches long, up to 3/4 inch wide, pointed at the tip, tapering to the nearly sessile base, usually smooth.
- Flowers: Many crowded in dense racemes, the racemes erect, up to 1 1/2 inches long, on smooth stalks.
- Sepals: Usually 5, united below, usually pinkish, up to 1/6 inch long.
- Petals: 0.
- Stamens: 6-9.
- Pistils: Ovary superior; styles usually 2.
- Fruits: Achenes triangular or sometimes flattened, 1/8-1/6 inch long, smooth, shiny.
- Notes: The distinctive blotch present on many of the leaves of the lady's thumb may also be present in other species of Polygonum. The achenes are eaten by waterfowl and small mammals.
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