Fern Flower

The Fern Flower is a rare variety of flowering fern the produces yellow blooms all summer until they turn bright red on the eve of Kupala.
The leaves contain a psychoactive drug and can be eaten or smoked for a powerful feeling of euphoria. It also allows the user to understand animal speech, spirits, and any language.
The flower can be eaten raw or brewed into a tea. It contains a mild aphrodisiac and causes the user to fall in love with anyone or anything they may encounter while under its influence.
Great for parties. Not recommended in high doses.

Disclaimer: This is my own interpretation, real information on the myth can be found here: [link]