Polygonum amphibium L.
Water smartweed, longroot smartweed, water knotweed, amphibious bistort
Water smartweed is native to much of North America, as well as Asia, Europe, and parts of Africa. Introduced elsewhere as well, it is sometimes considered a noxious weed.
Plants: Water smartweed roots extend thick stems which float or grow horizontally until they find a moist area, into which they extend new roots. Stems reach up to 9½′ (3 m) long and ⅜″ (1 cm) around.
Leaves: Leaves are 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 ⨉ ⅛–1¾″ (2–20 cm ⨉ 5–50 mm), with petioles 1/32–1″ (1–30 mm). Leaves are not mottled. Ocrea are ⅛–1¾″ (5–50 mm), with the upper part fringed with small hairs 1/32–⅛″ (0.5–4.5 mm) long.
Flowers: Flowers are 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.
Fruits: Tiny brown rounded achenes 1/16–⅛″ (2.5–3 mm) long. Each achene contains one seed. They appear from July to September.
Habitats: Floating in ponds, streams, and marshes. I first spied it while tubing down the Delaware river.
Edibility: Young shoots are edible if used sparingly. Like many plants, they contain oxalic acid, which contributes bitterness and is toxic if eaten often or in large quantities.
 |
Similar species. |
Online References:
References:
Clemants, Steven; Gracie, Carol, Wildflowers in the Field and Forest, Oxford University Press, 2006, p. 76
9/17/2023 · Sprague Pond Preserve, Basin Preserve, Phippsburg, Maine · ≈ 5 × 7″ (13 × 16 cm) 
9/14/2013 · Whitewater Rafting Trip, Barryville to Pond Eddy Leg, Delaware River, Barryville, Pennsylvania · ≈ 4 × 6″ (11 × 16 cm) 
8/16/2016 · John Tinker Trail, Nashua River, Groton, Massachusetts 
9/14/2013 · Whitewater Rafting Trip, Barryville to Pond Eddy Leg, Delaware River, Barryville, Pennsylvania · ≈ 4 × 6″ (10 × 14 cm) 
9/14/2013 · Whitewater Rafting Trip, Barryville to Pond Eddy Leg, Delaware River, Barryville, Pennsylvania · ≈ 2½ × 3½″ (7.3 × 9 cm) 
9/17/2023 · Sprague Pond Preserve, Basin Preserve, Phippsburg, Maine · ≈ 4½ × 7″ (11 × 16 cm) 
9/17/2023 · Sprague Pond Preserve, Basin Preserve, Phippsburg, Maine · ≈ 2½ × 3″ (6.4 × 8.4 cm) 
8/16/2016 · John Tinker Trail, Nashua River, Groton, Massachusetts 
9/14/2013 · Whitewater Rafting Trip, Barryville to Pond Eddy Leg, Delaware River, Barryville, Pennsylvania · ≈ 4 × 3½″ (10 × 9.2 cm) 
9/17/2023 · Sprague Pond Preserve, Basin Preserve, Phippsburg, Maine · ≈ 6 × 7″ (16 × 18 cm) 
8/16/2016 · John Tinker Trail, Nashua River, Groton, Massachusetts 
| Kingdom | Plantae | Plants, but not fungi, lichens, or algae (from Stearn's Botanical Latin) |
| Subkingdom | Tracheobionta | Vascular plants—plants with a “circulatory system” for delivering water and nutrients |
| Division | Magnoliophyta | Flowering plants, also known as angiosperms |
| Class | Magnoliopsida | Dicotyledons—plants with two initial seed leaves |
| Subclass | Caryophyllidae | Cacti, many other succulents, carnivorous plants, and leadworts |
| Order | Caryophyllales | Includes cacti, carnations, amaranths, ice plants, and many carnivorous plants |
| Family | Polygonaceae | Knotweed or smartweed family |
| Genus | Polygonum | Greek poly, “many,” and gonu, “knee,” for the swollen jointed stems |
| Species | amphibium | Amphibious, suited for or adapted to growing on land or in the water |
Polygonum amphibium description by Thomas H. Kent, not updated.
© FloraFinder.org. All rights reserved.