Root growth factor that regulates the pattern of root growth and lateral root development by modulating the length and the number of cortical cells in the root apical meristem (RAM), and the anticlinal asymmetric cell divisions in lateral root initiation cells. Extracellular signal peptide that regulates cell fate (PubMed:16489133). Represses root apical meristem maintenance (PubMed:16902140). Root growth factor that regulates the pattern of root growth and lateral root development (PubMed:22307643). Regulates the transition of protophloem cells from proliferation to differentiation, thus impinging on postembryonic growth capacity of the root meristem; this signaling pathway requires CRN and CLV2 (PubMed:28607033). Expressed in roots, leaves, siliques and seedlings. The tyrosine sulfation is critical for the function of the peptide. The O-glycosylation (arabinosylation) of the hydroxyproline Pro-43 enhances binding affinity of the CLE18p peptide for its receptor. Belongs to the CLV3/ESR signal peptide family.