An Arabidopsis cDNA clone that defines a new class of plant serine/threonine receptor kinases was found to be a member of a family of four clustered genes (lecRK-a1-a4) which have been cloned, sequenced and mapped on chromosome 3. This family belongs to a large superfamily encoding putative receptors with an extracellular domain homologous to legume lectins and appears to be conserved at least among dicots. In the Columbia ecotype only the lecRK-a1 and perhaps the lecRK-a3 gene is functional, since lecRK-a2 is disrupted by a Ty-copia retroelement and lecRK-a4 contains a frameshift mutation. Structural analysis of the lecRK-al and lecRK-a3 deduced amino-acid sequences suggests that the lectin domain is unlikely to be involved in binding monosaccharides but could interact with complex glycans and/or with hydrophobic ligands. Immunodetection of lecRK gene products in plasma membranes purified by free-flow electrophoresis showed that the lecRK-a proteins are probably highly glycosylated integral plasma membrane components.