Lythrum hyssopifolia

About

Lythrum hyssopifolia is a species of flowering plant in the loosestrife family known by the common names hyssop loosestrife and grass-poly. It is native to Europe but it is known elsewhere, including parts of Australia and eastern and western North America, as an introduced species and sometimes a weed. It is rare in the United Kingdom, with occasional isolated populations. It often grows in moist habitats, such as marshes and wet agricultural fields, rice paddies, for example.

Summary from Wikipedia