From Bulbapedia, the community-driven Pokémon encyclopedia.
The Remeyo weed underwater in the anime
Remeyo weed (Japanese: シレット水草 Shlet water herb) is a type of herbal medicine found exclusively in the anime. It grows on lake-beds and can be used to cure poison.
Some Water-type Pokémon are specifically trained just to be able to retrieve it. Ash used it to cure his, Iris's, and Cilan's Pokémon after they were poisoned by a group of wild Foongus in Facing Fear with Eyes Wide Open!.
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