A European species of loosestrife (Lysimachia vulgaris).(noun)
Any kind of Polygonum with willow-like foliage.(noun)
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Use "willow-weed" in a sentence
"All about grew tall, fruiting grasses, and many a bright flower; clusters of pink willow-weed, patches of yellow ragwort, the perfumed meadowsweet, and, amid bracken and bramble, the purple shining of a great campanula."