Is required for spatial control cell division during leaf development. Through an association with microtubules, acts both for the positioning of cytoskeletal arrays that establish planes of cell division during prophase and for spatial guidance of expanding phragmoplasts toward preestablished cortical division sites (CDS) during cytokinesis. Preferentially localized to the preprophase band (PPB) during mitotic division. Expressed in vegetative shoot tips consisting of leaf primordia and the bases of immature leaves, the shoot apical meristem, and unexpanded stem tissue. Strongly expressed in tissues enriched in dividing cells: ear primordia and embryos. Mutant tan1 displays a shorter stature with smaller, more erect leaves than normal. Moreover, mutant leaves have a distinctly roughened, crepe-papery texture compared to the smooth surface of a normal leaf.