Plant receptor kinases (RKs) enable perception of extracellular signals critical for growth, development, and environmental adaptation. Leucine-rich repeat RKs (LRR-RKs), the largest RK family, recognize diverse ligands, from small molecules to peptides, typically through recruitment of SERK-family co-receptors. However, the molecular basis of ligand specificity and co-receptor engagement across LRR-RK systems remains unclear. This work examines two structurally distinct signaling systems: brassinosteroid (BR) perception by BRI1/BRL1/BRL2/BRL3, and Casparian strip Integrity Factor (CIF) peptide perception by SGN3/GSO1 and GSO2. Using Grating-Coupled Interferometry binding assays and structure-guided mutagenesis, BR receptors were shown to bind chemically diverse hormones with high affinity, reflecting ligand-binding pocket plasticity, while SERK1 recruitment depends on specific ligand features independent of binding affinity. Similarly, SGN3/GSO1 and GSO2, despite high sequence identity, show distinct peptide-binding preferences and binding modes revealed by cryo-EM, with co-receptor recruitment governed by the peptide C-terminus. Together, these findings reveal how structurally divergent LRR-RKs achieve specific, high-affinity ligand and co-receptor interactions, offering a framework for engineering selective LRR-RK signaling antagonists.