Shakespeare was familiar with the wild pansy, or heart's ease, and the folklore surrounding it. In A Midsummer Night's Dream, Oberon instructs Puck:

"Yet mark'd I where the bolt of Cupid fell:
It fell upon a little western flower,
Before milk-white, now purple with love's wound
And maidens call it love-in-idleness.
Fetch me that flower; the herb I shew'd thee once:
The juice of it on sleeping eyelids laid
Will make or man or woman madly dote
Upon the next live creature that it sees."