dyer's knotweed; Persicaria tinctoria
A plant used historically to produce indigo dye. Often discussed in the context of traditional dyeing or botany.
See also: 藍
Dyer's knotweed was cultivated as a raw material for indigo dyeing.
Katakana spelling is common for plant names; usually written in kana.
Kanji spelling exists but is rarely used; the plant is usually referred to in kana.
Compound of 蓼 (たで, 'knotweed') and 藍 (あい, 'indigo'). The exact historical derivation is uncertain, but the name directly describes the plant's use in indigo production.