Pedagogical content knowledge (PCK) is a much debated and studied construct. In this article, we adopt an all-embracing view of PCK to examine the development of one elementary science teacher's knowledge over a 10-year period. We portray this teacher's knowledge at three critical points in her career--as a student teacher, beginning teacher, and established teacher--and represent and analyze the growth of her science PCK using the metaphor of a knowledge tree. The tree metaphor shows that while science knowledge begins as the major branch of science PCK, it is soon overshadowed by the general teaching and interactive knowledge branches of science PCK; however, taken together, all three branches contribute over time to the formation of a healthy, established tree of science PCK.