Burke: Polygonum aviculare vs. Polygonum paronychia

	Polygonum aviculare	Polygonum paronychia
		beach knotweed, black knotweed
Habit	Highly variable species, prostrate and spreading (but not rooting at the nodes) to occasionally erect, freely-branched annual, the stems terete, striate, up to 1 m. long.	Low, spreading shrub-like perennial here in Washington - typically less than 30 cm., though can get up to 100 cm. tall in some parts of its range.
Leaves	Numerous, bluish-green, only slightly reduced upward, narrowly oblong, 1-3 cm. long and 2-6 mm. broad, narrowed to a very short, jointed petiole; stipules lacerate, 3-6 mm. long.	Alternate, simple, narrow, 1-2 cm long, with prominent midrib.
Flowers	1-3 in the axils of the leaves or leaf-like bracts, the pedicles 1-3 mm. long, erect; perianth 2.5 mm. long, divided 2/3 the length, the segments 5, oblong, sub-equal, greenish with white to pink or red margins.	Small pinkish or whitish, 5-6 mm long, with 5 parts; in small clusters along stem.
Fruits	Achene with 3 sharp angles, brownish, smooth.	Shiny black achenes 4-5 mm long.

	Polygonum aviculare	Polygonum paronychia
Identification notes		Can be separated from other Polygonum species by its perennial decumbent stems, lacerate hyaline stipules, axillary flower clusters, and coastal habitat.
Flowering time	May-October	April-September
Habitat	Dry or slightly moist, disturbed soil, often where hard-packed.	Coastal shorelines and sand dunes.
Distribution	Occurring on both sides of the Cascades crest in Washington; Alaska to California, east across North America to the Atlantic Coast. [WildflowerSearch map] [BONAP county map]	Occurring west of the Cascades crest along the coast; Vancouver Island, B.C., south to Monterey, California. [WildflowerSearch map] [BONAP county map]
Origin	Both native and introduced	Native
Conservation status	Not of concern	Not of concern
Sibling taxa	P. achoreum, P. austiniae, P. californicum, P. douglasii, P. erectum, P. fowleri, P. majus, P. minimum, P. nuttallii, P. paronychia, P. parryi, P. polygaloides, P. ramosissimum, P. sawatchense, P. spergulariiforme	P. achoreum, P. austiniae, P. aviculare, P. californicum, P. douglasii, P. erectum, P. fowleri, P. majus, P. minimum, P. nuttallii, P. parryi, P. polygaloides, P. ramosissimum, P. sawatchense, P. spergulariiforme
Subordinate taxa	P. aviculare ssp. aviculare, P. aviculare ssp. buxiforme, P. aviculare ssp. depressum, P. aviculare ssp. neglectum
Web links	Local floras: BC, CA, OR, WA Local Web sites: CalFlora, CalPhotos, Flora NW, PNW Herbaria, Turner Photog. WildflowerSearch iNaturalist (observations) USDA Plants Database LBJ Wildflower Center SEINet Plants of the World Online Encyclopedia of Life Wikipedia Google Image Search	Local floras: BC, CA, OR, WA Local Web sites: CalFlora, CalPhotos, Flora NW, PNW Herbaria, Turner Photog. WildflowerSearch iNaturalist (observations) USDA Plants Database LBJ Wildflower Center SEINet Plants of the World Online Encyclopedia of Life Wikipedia Google Image Search

Polygonum aviculare

Polygonum paronychia

beach knotweed, black knotweed

Habit

Highly variable species, prostrate and spreading (but not rooting at the nodes) to occasionally erect, freely-branched annual, the stems terete, striate, up to 1 m. long.

Low, spreading shrub-like perennial here in Washington - typically less than 30 cm., though can get up to 100 cm. tall in some parts of its range.

Leaves

Numerous, bluish-green, only slightly reduced upward, narrowly oblong, 1-3 cm. long and 2-6 mm. broad, narrowed to a very short, jointed petiole;

stipules lacerate, 3-6 mm. long.

Alternate, simple, narrow, 1-2 cm long, with prominent midrib.

Flowers

1-3 in the axils of the leaves or leaf-like bracts, the pedicles 1-3 mm. long, erect;

perianth 2.5 mm. long, divided 2/3 the length, the segments 5, oblong, sub-equal, greenish with white to pink or red margins.

Small pinkish or whitish, 5-6 mm long, with 5 parts; in small clusters along stem.

Fruits

Achene with 3 sharp angles, brownish, smooth.

Shiny black achenes 4-5 mm long.

Polygonum aviculare

Polygonum paronychia

Identification notes

Can be separated from other Polygonum species by its perennial decumbent stems, lacerate hyaline stipules, axillary flower clusters, and coastal habitat.

Flowering time

May-October

April-September

Habitat

Dry or slightly moist, disturbed soil, often where hard-packed.

Coastal shorelines and sand dunes.

Distribution