Responsible for the deacetylation of lysine residues on the N-terminal part of the core histones (H2A, H2B, H3 and H4) (PubMed:23362208). Histone deacetylation gives a tag for epigenetic repression and plays an important role in transcriptional regulation, cell cycle progression and developmental events (Probable). Histone deacetylases act via the formation of large multiprotein complexes (Probable). Required for appropriate cellular patterning in the root epidermis (PubMed:16176989, PubMed:23362208). Involved in the differentiation of hair and non-hair cells in the root epidermis (PubMed:23362208). Is not directly involved in the regulation of the expression of pattern genes (PubMed:23362208). Regulates the transcription of certain kinase genes, which are components of a positional information relay system, by changing their histone acetylation status (PubMed:23362208). H2O + N(6)-acetyl-L-lysyl-[histone] = acetate + L-lysyl-[histone] Binds 1 zinc ion per subunit. Expressed in roots, stems, young rosette leaves, flowers and siliques. HDA5, a tandem duplication of HDA18, is not required for the cellular patterning in the root epidermis. Belongs to the histone deacetylase family. HD type 2 subfamily.