Stem cells in plants, better known as meristems, can determine the number and fate of cells, structure and fate of tissues, shape and type of organs, phases of plant vegetative and sexual reproduction, and general plant architecture. In this review I propose that, contrary to the common view, stem cells in plants in both their broad definition (all meristems) or even according to the narrower one (central part of the shoot and root apical initial-cell zone) are differentiated. I list the various plant meristems and discuss why they should be considered differentiated. I also discuss their alleged totipotency in vivo, the question of whether all plant cells are differentiated, the types of cell differentiation and the issue of re-differentiation by plant cells. The question of whether there are several types of stem cells in plants that differ in their level of “stemness” is also discussed. Plant meristems (including apical ones) are differentiated irom structural (they include several cell types) and functional points of view. Their various types of origin, many times following re-differentiation of other cell types also indicate that meristems are differentiated. Finally, now it is well established that their development and physiology depend on the up- or down-regulation of specific regulatory genes that induce stem cell production and regulate their amount. All these facts clearly indicate that they are differentiated and that they specialize in the production of new cells, tissues and organs.