water pepper (Persicaria hydropiper)
A plant species; also known as ヤナギタデ (柳蓼).
See also: ヤナギタデ (やなぎたで)
Water pepper is an annual plant that grows in wetlands.
Katakana spelling is common for plant names; usually written in kana.
Kanji spelling is rare; the word is usually written in kana.
Compound of 水 (mizu, 'water') and 蓼 (tade, 'knotweed, smartweed'). The exact derivation is uncertain, but the name likely refers to its habitat.