T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network

Polygonum aviculare (Wireweed,)

Kingdom:   Plantae
(Unranked):        Angiosperms
(Unranked):        Eudicots
(Unranked):        Core eudicots
Order:       Caryophyllales
Family:      Polygonaceae
Genus:      Polygonum
Species:     P. aviculare
Binomial name: Polygonum aviculare
Common name:  Wireweed, Knotgrass, Lowgrass, Common Knotgrass, Birdweed, Pigweed.

Polygonum aviculare is a plant related to buckwheat and dock. It is an annual herb with a semi-erect stem that may grow to 10 to 40 cm high. The leaves are hairless and short-stalked. They are longish-elliptical with short stalks and rounded bases; the upper ones are few and are linear and stalkless. The stipules are fused into a stem enclosing, translucent sheath known as an ochrea that is membranous and silvery. The flowers are regular, green with white or pink margins. Each has five perianth segments, overlapping at the base, five to eight stamens and three fused carpels. Flowering occurs during the summer months.
The fruit is a dark brown, three-edged nut. The seeds need light to germinate which is why this plant appears in disturbed soil in locations where its seeds may have lain dormant for years.
This plant has a wide distribution as an arable weed and is a plant of fields, shingle, sand, roadsides, yards and waste places. There are many morphological variations among different populations and several different sub-species are recognised.  

Thanks to Wikipedia for text and information: https://creativecommons.org/licenses/by-sa/3.0