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Polygonum amphibium

Polygonum amphibium L.

 

Water Smartweed, Longroot Smartweed, Water Knotweed, Amphibious Bistort

KingdomPlantaePlants, but not fungi, lichens, or algae
SubkingdomTracheobiontaVascular plants—plants with a “circulatory system” for delivering water and nutrients
DivisionMagnoliophytaFlowering plants, also known as angiosperms
ClassMagnoliopsidaDicotyledons—plants with two initial seed leaves
SubclassCaryophyllidaeCacti, many other succulents, carnivorous plants, and leadworts
OrderCaryophyllalesIncludes cacti, carnations, amaranths, ice plants, and many carnivorous plants
FamilyPolygonaceaeKnotweed or smartweed family
GenusPolygonumGreek poly, “many,” and gonu, “knee,” for the swollen jointed stems
SpeciesamphibiumAmphibious, suited for or adapted to growing on land or in the water

About plant names...

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. It is found floating in ponds, streams, and marshes. I first spied it while tubing down the Delaware river.

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).

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 can reach ⅛-1¾" (5-50 mm) in length.

Flowers: Flowers are pink, appearing in a dense oval cluster of tiny five-lobed flowers. The cluster is up to ½" (1.5 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.

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.

Online References:

Polygonum amphibium at the Washington State Department of Ecology

Polygonum amphibium on Wikipedia

Polygonum amphibium on Plants for a Future, a resource and information centre for edible and otherwise useful plants

Polygonum amphibium at the Lady Bird Johnson Wildflower Center

Polygonum amphibium on eFloras

Polygonum amphibium (Water Smartweed, Longroot Smartweed, Water Knotweed, Amphibious Bistort)

9/14/2013 · Whitewater Rafting Trip, Barryville to Pond Eddy Leg, Delaware River, Barryville, PA
≈ 4 × 6" (11 × 16 cm)

Polygonum amphibium (Water Smartweed, Longroot Smartweed, Water Knotweed, Amphibious Bistort)

8/16/2016 · John Tinker Trail, Nashua River, Groton, MA

Polygonum amphibium description by Thomas H. Kent, last updated 1 Jul 2017.

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Polygonum amphibium (Water Smartweed, Longroot Smartweed, Water Knotweed, Amphibious Bistort)

9/14/2013 · Whitewater Rafting Trip, Barryville to Pond Eddy Leg, Delaware River, Barryville, PA
≈ 4 × 6" (10 × 14 cm)

Polygonum amphibium (Water Smartweed, Longroot Smartweed, Water Knotweed, Amphibious Bistort)

9/14/2013 · Whitewater Rafting Trip, Barryville to Pond Eddy Leg, Delaware River, Barryville, PA
≈ 2½ × 3½" (7.3 × 9 cm)

Polygonum amphibium (Water Smartweed, Longroot Smartweed, Water Knotweed, Amphibious Bistort)

8/16/2016 · John Tinker Trail, Nashua River, Groton, MA

Polygonum amphibium (Water Smartweed, Longroot Smartweed, Water Knotweed, Amphibious Bistort)

9/14/2013 · Whitewater Rafting Trip, Barryville to Pond Eddy Leg, Delaware River, Barryville, PA
≈ 3½ × 4" (9.2 × 10 cm)

Polygonum amphibium (Water Smartweed, Longroot Smartweed, Water Knotweed, Amphibious Bistort)

8/16/2016 · John Tinker Trail, Nashua River, Groton, MA

Range:

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