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flourishing (of plants); thriving; luxuriant growth; growing lushly; rankness (of weeds)
雑草が繁茂して道が見えなくなった。
Weeds grew so thick that the path became invisible.
熱帯雨林は植物が繁茂する地域だ。
Tropical rainforests are regions where plants flourish.
手入れを怠ると草が繁茂してしまう。
If you neglect maintenance, grass will grow rampant.