*willow-herb*

n. (Bot.) A perennial herb (Epilobium spicatum) with narrow willowlike leaves and showy rose-purple flowers. The name is sometimes made to include other species of the same genus. [ 1913 Webster ]

Spiked willow-herb, a perennial herb (Lythrum Salicaria) with willowy leaves and spiked purplish flowers. [ 1913 Webster ]