The charismatic Macginitiea, a tree of the family Platanaceae, have a long fossil history throughout western North America ranging from at least the Paleocene to the late Eocene. Here, we describe a new species of Macginitiea from the early middle Eocene Flora of Kisinger Lakes. The new species has a surprising proclivity for developing basilaminar lobes. By observing the variability of Macginitiea, with special attention to its basilaminar traits, we expand our understanding of the genus, its rich history, and diversification patterns within the Platanaceae. Additionally, we explore the development of these traits in modern plants, which suggest the evolution of a complex gene regulatory network (GRN) that led to the high species diversity.