Plants are simpler organisms than animals, having three organ systems and fewer organs than do vertebrate animals. Organs are composed of tissues, which are in turn composed of cells. Functions include lining, protecting, and forming glands. Cuboidal epithelium is cube-shaped cells. Columnar epithelium consists of elongated cells.
Any epithelium can be simple or stratified.
Simple epithelium has only a single cell layer. Stratified epithelium has more than one layer of cells. Pseudostratified epithelium is a single layer of cells so shaped that they appear at first glance to form two layers. Note the single layer of simple cuboidal epithelium lining either side of a tubule. I have outlined one of the columnar epithelium cells.