Cell polarity is very important for plant development, as it gives the cell a sense of direction. However, we still do not understand exactly how polarity directs cellular processes. We investigated a new family of polar proteins, called SOSEKI. These proteins accumulate in specific cell edges, but it was unknown why they were there and how they evolved. We found protein domains that play a role in SOSEKI function and location, and the proteins revealed a plant-wide compass already visible in the embryo. SOSEKI arose in the first land plants and their cell edge accumulation might be an ancient trait. The domain responsible for protein clustering is even older: it has similar functions across kingdoms of life. Study of proteins that interact with SOSEKI allowed us to form a model of SOSEKI as a corner-based scaffold that recruits other proteins for local tasks. This work provided more understanding of the mechanisms and evolution of cell polarity.