Plants follow a fundamentally different process for growth than animals. For example, it would be odd (to say the least) to find a new limb forming on a person after embryonic development, yet plants produce nearly all of their form post-embryonically, with only a minimal set of body parts created during embryogenesis. The ability to continue producing organs after embryo formation demonstrates that much of plant growth is indeterminate, meaning a plant can continue producing new organs like leaves over and over. This strategy has proven to be flexible and adaptable across a wide range of ecosystems, allowing some plants to live for hundreds, or even thousands, of years.
In addition to indeterminate growth, plants also show a high degree of developmental plasticity. For an organism that is not free to run away from drought, cold, or herbivores, this attribute is an important strategy. No two plants ever look exactly the same because of this plasticity, and this property allows individuals to become tailor-made for their specific site, producing roots in just the right locations, avoiding rocks and other roots, and sending out branches with leaves right where they will intercept light.
There are, however, certain patterns that seem to be repeated when one looks closely at a plant. The spacing of leaves along a stem, for example, tends to follow a fairly repeatable pattern. This and other patterns indicate that development in plants is iterative, suggesting a pre-recorded program that repeats itself after a certain period.
Plant growth follows these three principles – it is indeterminate, plastic, and iterative. The application of these principles leads to the tremendous variety of forms we find in the plant kingdom, from the arrangement of petals in a flower to the spiral alignment of branches on a pine tree. And all of these arise from the organization of cells into form-producing factories known as meristems.