Animals have centrioles to form spindle fibers during prophase. The centriole divides cells. Plants do not have them because they have microtubules instead; they do not need centrioles. Plants are capable of forming a circular loop of microtubules around the future plane of division prior to prophase called the preprophase band, rather than centrosome. Basically- plants don't need it. They have a different way of cell division.