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Persicaria amphibiium var. emersum

Species category

Weed

Common name

water knotweed

Diagnostic characters

Planting unit

AcheneAchene:
A dry, hard, one-chambered, one-seeded indehiscent fruit, as in buckwheat (Fagopyrum) or sunflower (Helianthus). The fruit wall is not united with the seed coat.

Shape

OvalOval:
Broadly elliptic.

Size

  • Length 2.2–2.8 mm 
  • Width 2–2.2 mm 
  • Thickness 1.5 mm 

Color

Black

Texture

Minutely rough

Other structures

Remnants of floral parts at the base. ApexApical:
The distal end of the fruit or seed away from the point of attachment or attachment scar.
 pointed.

Identification notes

AcheneAchene:
A dry, hard, one-chambered, one-seeded indehiscent fruit, as in buckwheat (Fagopyrum) or sunflower (Helianthus). The fruit wall is not united with the seed coat.
 is two-sided, with one side convex and the other flat (plano-convex).

Noxious weed seed categories

Not listed

AOSA examination list

Not included

Nomenclature

Family

Polygonaceae

Valid name

Persicaria amphibium L. var. emersum (Michx.) J.C. Hickman

Synonyms

Persicaria amphibia (L.) Gray p.p.
Persicaria coccinea (Muhl. ex Willd.) Greene
Persicaria muehlenbergii (S. Watson) Small
Polygonum amphibium L. var. coccineum (Muhl. ex Willd.) Farw. Polygonum amphibium L. var. emersum Michx. Polygonum coccineum Muhl. ex Willd.
Polygonum coccineum Muhl. ex Willd. var. pratincola (Greene) Stanford
Polygonum coccineum Muhl. ex Willd. var. terrestre Willd.
Polygonum muehlenbergii S. Watson
Polygonum muehlenbergii S. Watson var. terrestre (Willd.) Trel.

Polygonum amphibium var. emersum . Achenes with remnants of floral parts at the base and a pointed apex. 
Polygonum amphibium var. emersum. Achenes with remnants of floral parts at the base and a pointed apex.