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

Persicaria hydropiper (Water pepper)

Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Core eudicots
Order: Caryophyllales
Family: Polygonaceae
Genus: Persicaria
Species: P. hydropiper
Binomial name: Persicaria hydropiper
Synonym: Polygonum hydropiper
Common names: Water-pepper, Water pepper, Marshpepper knotweed, water-pepper smartweed

Persicaria hydropiper is an anthropogenic (disturbed habitats), summer annual of meadows and fields, shores of rivers or lakes, swamps, wetland margins. It is a widespread plant, found in Australia, New Zealand, temperate Asia, Europe, and North America.
It is an annual herb with an erect stem growing to a height of 20 to 70 cm. The simple leaves are alternate and almost stalkless. The leaf blades are narrowly ovate and have entire margins fringed by very short hairs. On mature plants, the margins may be wavy. They are tapering with a blunt apex. Each leaf base has stipules which are fused into a stem enclosing sheath that is loose and fringed at the upper end.
The inflorescence is a nodding spike. The perianth of each tiny flower consists of four or five segments, united near its green base and white or pink at the edges. There are six stamens, three fused carpels and three styles. The fruit is a dark brown oval, flattened nut.
Because leaves are quite acrid livestock appear to dislike eating it.

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