Final answer:
Nehemiah Grew established the study of plant anatomy, focusing on the cellular structure and organization of plant tissues.
Step-by-step explanation:
The scientific pioneer who established the study of the internal structure of plants known as plant anatomy was Nehemiah Grew. This field focuses on the cellular structure and tissue organization in plants. While other scientists like Carolus Linnaeus made significant contributions to taxonomy and Johann Gregor Mendel to genetics, it was Nehemiah Grew who is regarded as one of the founders of plant anatomy through his detailed studies of plant tissues.