One of Shakespeare's most famous love potions is used by the fairy Puck in A Midsummer Night’s Dream, and made from a flower called ‘love-in-idleness’, otherwise known as the wild pansy (Viola tricola).
The potion is created when Cupid shoots an arrow at 'the imperial votaress' (Queen Elizabeth I), but misses and instead hits the flower. The petals turn from white to purple, and the flower's juice becomes a love potion. Puck then places the potion on the sleeping eyes of Lysander, and later Demetrius which causes chaos in the forest.
In the natural world, petal colour is an important feature of plants, as insects use petal designs to determine where they should land to collect nectar. Many insects can also see a broader spectrum of light than humans including ultraviolet, which means that flowers look significantly different in 'insect view'.
Scientifically speaking, viola tricolor is not able to induce love, but extracts from the plant have been shown to be anti-microbial and cytotoxic. Cytotoxic chemicals can kill whole cells so may be able to treat diseases caused by uncontrolled growth, like cancers.
There does however exist a 'love hormone' known as oxytocin which can foster feelings of love or affection in humans, and the hormone dopamine which is released when we kiss, has been found to stimulate the same areas of the brain as heroin and cocaine.