The Paveisiejai triangular oak tree is a botanical natural heritage object, an oak tree of exceptional age and dimensions, growing in the village of Paveisiejai in the Lazdijai district, Veisiejai municipality. In 2012 it was declared a state protected area. The monumental tree stands about 1.5 kilometres south-west of the village of Petroškai. The oak tree branches into three trunks at a height of 2 metres from the ground. The height of the tree is 30 metres.