Each plant organ originally evolved in the context of specific environmental imperatives related to terrestrial life. Roots anchor the plant and also absorb water and mineral nutrients. Leaves were adapted to optimize photosynthesis. Stems elevate the leaves, serve as a conduit from the roots to the leaves, and also generate new growth. However, each linage of plants have followed their own unique evolutionary path through time, and in many plant groups stems roots and leaves have become secondarily modified by natural selection in unusual and surprising ways.