Plant taxonomy: Organising the diversity of nature

Botany is divided into disciplines, Morphology, Anatomy, Physiology, Ecology, Pathology, Ethnobotany/Economic Botany, Algology, Bryology/Pteridology (Lower green plants), Palynology/Palaeobotany and Plant Taxonomy (Systematic Botany). Emerging areas in Botany include the Environmental and Forensic botany as well as Molecular systematics. Plants can now be studied at the molecular level, obtaining data from chemicals (chemotaxonomy) which makes use of proteins, carbohydrates and enzymes and other molecules with the use of chromatographic methods to the use of DNA (the genetic material) which can be extracted by several methods and sequenced to produce nucleotides or bases. This has allowed an improved knowledge of the evolutionary relationships among different plants and plant groups resulting in the re-ordering or re-arrangement of several plant taxa. On whether these efforts of the “omega taxonomy” would stand the test of time when compared with the “alpha taxonomic study” only the future will tell.

Apart from being very crucial to our existence, plants even control our climate and are the major indices of climate change. There are different types of plants; the non flowering and the flowering, the seed and the seedless, the green and non-green, vascular and the non-vascular depending on the criterion for classification.

The concept of flower or what constitutes a flower may be debatable. To some people the flower has a structure containing sepals, petals, stamens and carpels.

 

Voyage into Plant taxonomy

My first exposure to Plant taxonomy was in BOT 303 (Angiosperm Taxonomy) in the then University of Ife, Ile-Ife in 1984 with Professor Omotoye Olorode. In his characteristic manner, if we could not identify plants, especially common ones, he would give a lecture within a lecture as to the reason why we should go back to our villages to learn about plants in our environment. It was thus a herculean task passing that course. Thereafter, I prayed never to have anything to do with Plant Taxonomy again. When I was to seek admission into the University of Lagos for my Masters programme, the closest to my desired discipline (Plant Anatomy) was Plant taxonomy. As there was no Plant Anatomist then in the Department, I was confronted with my “enemy” once again. Being desperately in need of the admission, I had to apply and consequently register for the programme upon admission. As fate would have it, I met my mentor, Professor J. D. Olowokudejo as my supervisor who subsequently transcribed the genes for this discipline into me. To the glory of God here I am today, delivering this lecture as a Professor in a supposedly dry and difficult but interesting field of science

 

Ordering of nature: Biblical perspective

Botanists are the favourites of God, because they are the ones to whom God entrusted the first living creatures (Plants). After the creation of light, the waters and the dry land, God created vegetation (Genesis 1:11-13). God said “let the earth produce vegetation, seed bearing plants, fruit trees bearing fruit with seed, each according to its kind upon the earth. And so it was. God saw that it was good.” That was on the third day. God did not create any animal until the fifth day.  So the creation of plants predated that of animals and man. The plants were to give the life of God to the animals. We humans are the highest of these animals in hierarchy and cannot survive without the plants.

 

Biodiversity and Plant Taxonomy

According to the United Nation Convention on biodiversity, people value biodiversity in different ways. It might be spiritual, economical, aesthetical, cultural or scientific. Biodiversity values also differ at international (based on global concern for maintaining the existing species richness on earth), at national (in relation to economic benefits brought about by activities such as harvesting of timber, hunting and tourism) and at the local level (as the primary sources of livelihood; for medicine, food, clothing, shelter, and other products).

It is therefore disheartening to note that while aggressive floristic studies are going on in the world especially in Europe, America and Asia, Africa in general and Nigeria in particular are lagging behind. Most records of our flora today in Nigeria were derived from the collections of early explorers and bequeathed to us by our colonial masters. Their efforts as plant collectors in West Africa often resulted in many of them paying the supreme price – death.

My experience in field work can be summarized in the words of St Paul in his second letter to the Corinthians 4:8-10. I was often troubled, but not crushed; sometimes in doubt, but never despaired, there were many enemies among the plants and animals but I was never without friends among them; and though badly hurt at times but I was not destroyed. However, the hazards and daunting experiences I encountered during my field trips cannot be compared to those of the early plant collectors. A striking and pitiable example is that of David Douglas. Douglas, an indomitable Scottish botanist led many collecting trips to North America. He was attacked by native American Indians bears, suffered all sorts of diseases and he twice had to eat his horse to avoid starvation (Moore et al., 1998).

If we must fully harness the potentials of plants in Nigeria, we need to promote intensive floristic studies from time to time. This will enable us break the diversity of plants into comprehensible groups based on the similarities and differences of characters among members of each group. Such ordering of plants into groups is called classification. Having classified the plants, any unknown plant can be assigned to any of the groups previously created or allotted to a new group if it does not fit into any existing group. This is done by comparing the characteristics of the unknown plant with those of different groups. This is called identification. Finally, there must be a means of communication on any plant in any of the groups by attaching a name to it. This is the Naming of plants or Nomenclature. This is why some authors define Plant taxonomy as the study of classification, identification and nomenclature or as the study of the principles and practice of classification.

Classification, identification and the naming of plants (Taxonomist and taxonomic activities)

It is now time to introduce you to the activities of the Plant taxonomist. This is with the aim of changing the mindset of many who believe that taxonomy is all about names of organisms. I have tried to find out from my students who do not signify interest in Plant taxonomy as to the reasons for their attitude. Their usual reaction is “How am I expected to know and keep all names of plants in my brain as if I do not have other things to do.” My answer has always been that “taxonomy is not only about botanical names; and there are different methods of identification which do not entail cramming of names.” Actually, not only plant taxonomists can provide the names of plants. Others, especially field workers, who are not even scientists do and effectively too. But they do this by overall familiarity with the plants they identify. They may lack necessary skills when confronted with entirely new plants, especially from new areas. This is where the taxonomist comes in; especially in the skilled use of the KEY, a major instrument of identification.

 

My contributions to Plant taxonomy and systematics

Mr Vice-Chancellor Sir, in my quest to revise many plant taxa in Nigeria and West Africa, I have made use of some of the markers mentioned above particularly anatomy, chemistry, pollen and morphology. Before my audience is lost in the proceeding illustration of my activities, let me state that a taxon (plural taxa) is any taxonomic rank or group to which a plant is assigned. The main or principal ranks e.g. the Species, Genus, Family, Order, Class, Division/Phylum and the Kingdom have been listed earlier in this lecture. What then is a Revision or why the need for revision? Revision is a reassessment of the taxa of a region, sub region, province or country with a view to unravelling the evolutionary influence and consequences in the group after a period of time. In revisions, new species may be discovered, current species may be split, others may be merged, species may be transferred to other taxa or new groups created. Revision presents the current taxonomic knowledge about the taxa under study and helps to determine the taxonomic relationships among the taxa. This activity of the taxonomist sometimes contributes to the changes in plant names. Revision enables us to detect evolution at work as stated in the definition of Plant taxonomy earlier in this lecture.

I started the revision of the family Polygonaceae when little was known about the taxon  in Nigeria. Collections were made from several parts of Nigeria including the Mambilla plateau. Morphological markers employed elucidated the taxonomic relationships among and within taxa in this family.

Being excerpts of an inaugural lecture delivered by Professor Abiodun Ayodele at the University of Ibadan, Ibadan.