An unknown plant arrived in our garden, no doubt by courtesy of a passing bird, early on this year. It is about 850mm (33.5") tall. (See attached photos) Would anyone know what it is? Also, is that three lobed structure between the flowers a seed pod?
Welcome Drosilla. It is a Euphorbia. Yes the 3 lobed thing is the seed pod. Be careful of the sap it can cause skin irritation.
Euphorbia lathyris (Caper Spurge) An invasive weed, and, as Luddite mentions, caustic / poisonous sap.