Receptor-like protein kinase required for cell elongation during vegetative growth, mostly in a brassinosteroid-(BR-) independent manner. Expressed in most vegetative tissues, including leaves, stems and roots, especially in cell elongation regions. By brassinosteroids (BR). Autophosphorylated. No visible phenotype; due to redundancy with THE1. Herk1 and the1 double mutants are stunted. In herk1-1, shorter hypocotyls without brassinolide (BL) treatment than with BL treatment. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.