Complex cell-to-cell communication between the male pollen tube and the female reproductive organs is required for plant fertilization. A family ofCatharanthus roseusreceptor kinase 1-like (CrRLK1L) membrane receptors has been genetically implicated in this process. Here, crystal structures of theCrRLK1Ls ANXUR1 and ANXUR2 are reported at 1.48 and 1.1 Å resolution, respectively. The structures reveal a novel arrangement of two malectin-like domains connected by a short β-hairpin linker and stabilized by calcium ions. The canonical carbohydrate-interaction surfaces of related animal and bacterial carbohydrate-binding modules are not conserved in plantCrRLK1Ls. In line with this, the binding of chemically diverse oligosaccharides to ANXUR1 and HERCULES1 could not be detected. Instead,CrRLK1Ls have evolved a protein–protein interface between their malectin domains which forms a deep cleft lined by highly conserved aromatic and polar residues. Analysis of the glycosylation patterns of differentCrRLK1Ls and their oligomeric states suggests that this cleft could resemble a binding site for a ligand required for receptor activation ofCrRLK1Ls.