The past 15 years have brought a revolution in biology with the wide application of molecular techniques in studies on the diversity and evolution of organisms. This catapulted us into a completely new era of biology.
We now realize the need to know much more about the structure of plants. In the hierarchy of structure, from molecules up to organelles, cells, tissues, organs, and organisms, one may assume that the structure of organisms, morphology in the classical sense, is the best known level because whole plants can be seen with the naked eye. However, as it is the most complex level, it is therefore also, in some way, the most difficult to understand. And although paradoxical, our knowledge of the morphology of plants currently has great deficits.
Morphology originally developed as a descriptive science to recognize and distinguish the diversity of plants, an aspect which obviously is always of great practical importance. However, from our current perspective, this represents only a narrow aspect of morphology.
The study of plant structure, ‘morphology’ in the wide sense, considers relationships between plant form and other levels of the structural hierarchy (anatomy, histology, cytology). Plant form is not restricted to outer surfaces. Flowers also have inner surfaces as they are intricately synorganized systems of original structural elements that are fused in various ways.
Additionally, morphology also encompasses development: the development of plant parts, but also whole plant development, which, in turn, helps us to better understand mutual relations of the individual parts. Knowledge of development helps us to better understand mature structures, which are often complex. Whole plant development is also necessary to better understand the plasticity of plant form in individuals, as, in contrast to animals, plants produce new organs throughout their life and the structure of these organs may vary depending on the environment.
Another aspect of plant structure is diversity and its evolution. We now have a much better idea of plant relationships than we did 15 years ago due to the advances of molecular techniques. In the past few years many major clades surfaced that had never been comparatively studied before. It will be important to study the morphology of all these new clades in order to reveal the features they share, and to gain a better understanding of their biology and the way these features have evolved. It is of little help if we just know taxon names and how these taxa are interrelated. Right now we have more bones than flesh. Better knowledge of morphology will fill this “skeleton” with life.
The actual aspects of structure that are of particular interest change throughout the hierarchy of diversity, and it may be quite different at the level of populations, species, genera, families, orders, and so on. At the level of populations, simple measurements of unproblematical morphological entities, morphometrics, are important. However, the higher we ascend up in the hierarchy of diversity, the more we find structures that are difficult to interpret, and the more important the resolution of homologies becomes. This is a particularly exciting process and requires a multifaceted integrative approach.
Thus morphology includes the aspects of development and evolution. Plants cannot just aquire any thinkable form. Rather, there are inner limitations due to rules of development (morphogenesis) and outer limitations due to ecological factors. An ultimate goal would be to better understand the evolutionary interrelationships between these inner and outer limitations.
Thus morphology is a multidimensional key discipline in plant biology, with relationships to several other fields, such as:
- development of structure and molecular developmental genetics
- diversity of structure and evolution of plants
- Evo-Devo (which combines evolution and development)
- structure and systematics
- floral structure and reproductive biology
- structure and ecology
- structure and vegetation
- structure and biomechanics
- structure and systems biology.
It is to be expected that plant morphology based on many new tools and an integrative approach will successfully grow in the near future.
Peter K. Endress, University of Zurich