When the common name of a plant ends with the word "wort" this is because it was once perceived to have a medicinal use. This cheery little weed/wildflower is Lapsana communis, commonly known as Nipplewort.
 It was reputed to be efficacious in the event of sore nipples but I haven't had occasion to put it to the test. If any readers of this diary can vouch for the curative powers of Nipplewort please let me know.