Significance Due to the vital role for eukaryotes, clathrin-mediated endocytosis (CME) has attracted increasing attention, but great challenges still stand. Here, by overcoming the biggest challenge in CME research, we visualized the dynamic of extracellular cargo receptor protein by using stimulated emission depletion microscopy. We identified an unconventional mechanism for extracellular cargoes, here specifically rare earth elements (REEs). We showed that arabinogalactan proteins (AGPs) act as extracellular cargo receptors and move across the plasma membrane to initiate endocytosis. REEs promote the cross-membrane translocation of its extracellular cargo receptor AGPs to activate their endocytosis. Our data thus provide insights into the mechanism for the activation of CME, the biological role of AGPs, and the cellular mechanisms of REE actions in plants.