Designs and patterns in nature are not only aesthetically pleasing, but they also arouse curiosity. Why do such patterns exist? Are they essential for function? How are patterns established? Patterns are found at all biological levels, from ecosystems to molecules, and tools used to assess pattern at one level may be useful in understanding pattern at other levels. For example, ecologists have long used nearest neighbor analysis to understand plant communities; I and others have used such analysis to understand stomatal pattern, and molecular biologists now apply this method to understand genomic evolution. What is important is the realization by researchers at other levels that such analysis may be useful in understanding their problem.
This paper examines stomatal distribution as a pattern for study and is not concerned with differentiation of stomata and stomatal complexes, except for those cells that enter the stomatal pathway, but fail to fully differentiate. Stomata are well suited for investigation because the patterns are two dimensional, which simplifies analysis, and because stomata occur on organ surfaces, which makes them readily accessible. In spite of these advantages, information on stomatal patterning is sparse. Likewise, information on trichome patterning is also limited, in spite of growing molecular information on trichome differentiation. While trichome and stomatal patterning might be considered together in a paper on epidermal patterning, I choose to highlight stomatal patterning and present information in depth on these critically important cells, stomata.
In this paper, I provide a broad context for understanding pattern because I believe it is an essential backdrop necessary to understand theories and possible mechanisms of patterning. Stomatal patterning can be considered from many different reference points and based on these varied perspectives, I pose a number of questions to which we do not have the answers. I ask these questions to stimulate the community of researchers and suggest an avenue of study to tackle important problems in stomatal patterning. I begin first with a general discussion of pattern and common means by which stomatal pattern is assessed (see below, Pattern and Pattern Assessment). Stomatal patterning cannot be considered in isolation, but needs to be understood in terms of evolution, physiology, and organ form (Stomatal Pattern and Evolution, Stomatal Pattern and Physiology, Stomatal Pattern and Organ Form). Next, monocot and dicot leaf growth are reviewed and followed by existing theories explaining stomatal patterning in these two groups (Stomatal Patterning in Angiosperms). Lastly, I propose a unifying theory of stomatal patterning in Angiosperms, with a heading of the same name, followed by a brief summary.