During the time I have worked with plants, I have met many botanists and taxonomists and I particularly had the opportunity to associate closely with one of the most prominent in succulent plant taxonomy. I could never hope to emulate the energy, application, thoroughness and zeal with which that person approached the subject, nor the academic and written achievements. The sharing of ideas was however, a problem and I never felt much more than student. My discomfort with the taxonomic product of this persons work eventually resulted in alienation and eventually I wrote in frustration…”Taxonomy as a science has to answer the question “Are species real?” starting and ending with proper definition of the word/concept.”
The reply I received was this…”Yes, species are real, and defined well by their ability to cross freely and produce offspring which again crosses freely. This has been studied and demonstrated since 1750 or so (you may remember that I talked about this in one of our discussions on the subject), but it is naturally not easy to dive into so much work including following up several generations etc. And since related individuals are similar looking, the reciprocal conclusions that similar objects are related has unfortunately been used as being true, which it is not. And yet, species are the only natural unit in the whole of taxonomy, which to determine is the crucial point.
Perhaps this sounds rather like the famous Dicta of Bessey, but after having dealt extensively over 38 years by now with species boundaries in teaching, reading, theory and practice, in different vegetation zones and many different groups, I come back to old definition first given by Ray in 1682:
“Group of plants derived from common seeds, reproducing their typical features by sowing”
and used by most taxonomists since.
The point I have been trying to make in writing about Haworthia is that consciously or unconsciously, this definition describes the underlying perceptions of most persons. The very problem is the use of this simplistic definition and the fact that it does not work. I do not think I have ever been able to argue this adequately and this response from this paragon of academic botany leads me to this response. The Ray definition of the species flies in the very face of Darwin’s concept of their evolution and adaptation. If species did in fact breed true, there would be no adaptation and no evolution. The nature of creation is change and living things have the capacity in terms of inherent variability to meet this constant change whether it is by slow degree or by cataclysmic event. My contention is that “most taxonomists” have indeed thus been using a faulty definition and wholly underestimate the degree of variability in plants. Their contention may be that they are only providing an approximation of the truth, but this is not the effect achieved nor is it the impression I obtained from long association with this particular taxonomist and others. In Haworthia particularly, variation is pronounced. In some populations where field examination may suggest the plants are all very similar, when grown from seed no two individuals look alike. Vegetative propagation may have contributed to an illusion that plants breed true.
My own definition is that species are a dynamic and fractal group, or groups, of living or past living organisms which are morphologically, genetically and behaviorally continuous in space and time. Quite obviously the discontinuities are not going to be any easier to determine whether one uses Ray’s definition or mine. But what mine does is that it covers the reality that species are spread in geographic space and they have both the variability associated with the range of habitats they occupy as well as the inherent variability which provides them with the flexibility to respond to changes in habitat. Few people have the necessary experience in the field with enough living systems, and with cultivation, to truly encounter the phenomenal variability which underlies capacity to adapt and change