Unfurled palm leaf of an unidentified palm tree (family Palmae). Palm leaves are formed one at a time in a bud at the top of the plant's stem. Each leaf is composed of many small leaflets, which develop in the bud. As the mature leaf is unfurled from the bud, swellings develop which push the folded leaflets out into position. Before it opens, cells on the outside of the leaf often divide to form hairs. These provide a loose surface layer which acts as a lubricant during the opening of the leaf.