Taking my from my back yard for my first flower post - greater celadine (chelidonium majus) from the poppy family (papaveraceae). It's not native to my area but it has been naturalized in North America.
The poppy family is known for producing a sap: white, yellow or red
From the wiki, its yellow sap seems to have a history as a topical treatment for warts and similar skin conditions, but looks like current research is lacking.