Here's why:

* Stem cells are found in animals, including humans. They are undifferentiated cells that have the potential to develop into any type of cell in the body.

* Plant cells have unique characteristics like cell walls made of cellulose, chloroplasts for photosynthesis, and large vacuoles. Stem cells lack these features.

* Plants have their own type of stem cells called meristematic cells. These cells are responsible for the growth and development of plant tissues.

So, while both stem cells and meristematic cells are undifferentiated cells with the potential to develop into different cell types, they are distinct and belong to different kingdoms (animal and plant, respectively).