Northern Prairie Wildlife Research Center
Northeast Wetland Flora
Field Office Guide to Plant Species
Polygonum opelousanum Riddell
- Family: Smartweed (Polygonaceae)
- Flowering: July-October
- Field Marks: The distinguishing features of this Polygonum are the bristly sheaths, the
absence of glandular dots on the sepals, the smooth leaves, and the white or greenish
The achene beak is slightly exserted beyond the sepals at maturity.
- Habitat: Wet shores, damp thickets, sometimes in shallow standing water.
- Habit: Perennial herb from extensive creeping rhizomes.
- Stems: Upright to spreading, often rooting at the lower nodes, branched or unbranched, smooth or nearly so, up to 3 feet tall.
- Leaves: Alternate, simple, linear-lanceolate to lanceolate, pointed at the tip, tapering to the sessile or nearly sessile base, without teeth, usually ciliate along the margins, up to 4 inches long, up to 1 inch wide; sheaths with bristles.
- Flowers: Many loosely arranged into racemes, the racemes up to 2 1/2 inches long; each flower short-stalked.
- Sepals: 5, united below, white, greenish white, or greenish purple, up to 1/8 inch long, not glandular-dotted, persistent on the fruit.
- Petals: 0.
- Stamens: Usually 8.
- Pistils: Ovary superior; styles 3-parted.
- Fruits: Achenes triangular, ovoid to obovoid, shining, smooth, black, up to 1/8 inch long, partly exserted from the persistent sepals.
- Notes: This species is very similar to P. hydropiperoides and frequently is considered a variety of it. These two species are distinguished only in that the beak of the mature achene of P. opelousanum is slightly exserted beyond the incurved sepals.
The beak of P. hydropiperoides is completely enclosed within the sepals. The achenes are earen by waterfowl.
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