Polygonum amphibium (water smartweed)

Polygonum amphibium L.

Water smartweed, longroot smartweed, water knotweed, amphibious bistort

Kingdom	Plantae	Plants, but not fungi, lichens, or algae
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

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

9/14/2013 · Whitewater Rafting Trip, Barryville to Pond Eddy Leg, Delaware River, Barryville, PA
≈ 4 × 7" (11 × 16 cm)

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

Polygonum amphibium description by Thomas H. Kent, last updated 25 May 2020.

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

9/14/2013 · Whitewater Rafting Trip, Barryville to Pond Eddy Leg, Delaware River, Barryville, PA
≈ 3 × 3½" (7.3 × 9.0 cm)

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

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

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

Range:

About this map...