The Collaborative International Dictionary
Willow-weed \Wil"low-weed`\, n. (Bot.)
A European species of loosestrife ( Lysimachia vulgaris).
Any kind of Polygonum with willowlike foliage.
Wikipedia
Lysimachia vulgaris (garden loosestrife, yellow loosestrife, or garden yellow loosestrife) is a species of herbaceous perennial plants in the genus Lysimachia native to wetlands, damp meadows and forests of Eurasia. It is a 50–150 cm tall plant with an upright habit, blooming from June through August with erect panicles of conspicuous yellow flowers. L. vulgaris is sometimes considered invasive outside of its native range. In Australia growers have now successfully propagated and started growing the white variety in January in Tasmania.
Usage examples of "lysimachia vulgaris".
Besides the Cowslip and the Primrose, this family includes the little Scarlet Pimpernel (Anagallis), as truly a herald of warm summer weather as the Primrose is of spring, the Yellow Loosestrife and the Moneywort (Lysimachia vulgaris and Nummularia), the handsome Water Violet (Hottonia) and the nodding Cyclamen or Sowbread, all of which have medicinal value to a greater or lesser degree.