A liver tonic

This is a liverwort a member of an ancient group of plants. There are around 9000 species, they enjoy a worldwide distribution and they have existed for 400 million years. I reckon that makes them a most successful group! This one might be the Crescent Cup Liverwort Lunularia cruciata.

Their name derives from their lobed, liver-shaped leaves. In past times plants used as medicines were often known as wort; liverworts were, as you might imagine, thought to be most effective against liver disorders. 

Most liverworts can reproduce vegetatively (without any need for messy sex); when drops of water hit the raised cups on the liverwort's surface, tiny pieces of tissue called gemmae are splashed out.  If they land in a moist area, the gemmae will grow into new plants.