Have a look at a leaf. It may be helpful and fun to get a real leaf and have a look at it rather than just considering a mental image. Examining the leaf, a pattern can be seen clearly. Though, in drawing up such a structure, we would miss some of the lateral connections. Also, there are underlying patterns which inform all levels of natural systems, and which are only hinted at by the diagram.
Plants grow according to a genetic pattern, organic molecules are highly organised structures.
It tries to show that the leaf is embedded in a complex matrix of dependencies and connections, some of which may overlap. It must, of course, be emphasized, that all such maps must remain provisional - they simply can't represent the complexity of natural systems. These patterns are not static, but unfold over time . These patterns are goal-seeking , or stochastic systems. The pattern for the leaf is only a part of the pattern for a plant.