Taxonomic classification organisms and IPPC coverage of plants,
including and agreed interpretation of the term “plants”
Taxonomic classification of organisms and IPPC coverage of plants, including an agreed interpretation of the term “plants”
(prepared by Ian Smith)
Secretariat note: the Standards Committee (SC) requested that the TPG produces a document on the taxonomic classification of organisms, such as algae, bryophytes and fungi, and IPPC coverage of plants, including an agreed interpretation of the term “plants”. This document should be reviewed by the TPG and, when agreed, be presented to the SC.
What are “plants” for the IPPC?
There has never been a clear definition of what is to be understood by “plants” in the IPPC. Originally, the emphasis was on plants which are exploited for economic reasons by man, and which need to be protected from pests carried to new areas by international trade. In practice, this meant angiosperms, gymnosperms and pteridophytes (broadly “higher” or “vascular” plants). Yet the concept of plants at that time extended to bryophytes, algae, fungi and even bacteria, indeed everything that was not animal. This was reflected in the fact that the same Code of botanical nomenclature applied to all these organisms. In practice, the direct economic importance of these various other “plants” was not very great, nor did they need to be protected against the introduction and spread of pests.
The IPPC also potentially considers plants as possible pests of other plants. Higher plants are indeed potential weeds. But the other groups can be considered as insignificant, or else as potential “pathogenic agents” as in the Glossary definition of “pest”.
In the 21st century, the classification of organisms into kingdoms has greatly changed. There are no longer just the two kingdoms Animalia and Plantae, but at least seven (Archaea, Bacteria, Animalia, Protozoa, Chromista, Fungi, Plantae). A fuller account of the changes is presented in Appendix 1. It should particularly be noted that the new kingdoms principally concern organisms which used to be treated as plants: the prokaryotic Archaea and Bacteria, now seen as a completely different branch of living organisms; the fungi (including lichens); the “algae”, previously treated as groups of lower plants, but now redistributed between different kingdoms (though some remain as plants).
Does this affect the IPPC?
Various ISPMs now make it clear that the IPPC is also concerned with the protection of plants in the natural environment, insofar as these have a direct or indirect economic importance. The scope of the IPPC is potentially thus enlarged to that of the Convention on Biodiversity (CBD). In practice, the CBD is applied to macro-organisms, and countries take measures to protect endangered species of bryophytes, lichens, macrofungi, macroalgae, as well as higher plants. These organisms thus potentially fall under the scope of the IPPC also. At the present time, microorganisms are not individually targeted for protection, though their habitats might be. This is because:
many microorganisms are known to have a cosmopolitan, or near cosmopolitan, distribution
the distribution of many other microorganisms is poorly known
it is not clear what protective measures could be taken for endangered microorganisms.
Accordingly, the IPPC is not currently concerned with the protection of microorganisms.
There have also been changes in macro-organisms which are economically exploited and, in particular, in their international trade. Fungi are harvested and sold in much greater diversity than in the past, and traded internationally. Certain algae which have been exploited to a limited extent in the past, or only in limited areas of the world (particularly the Far East), are now grown more widely, internationally traded, and exposed to risks from international trade.
The recent International Botanical Congress in Melbourne (July 2011) has renamed the Code of botanical nomenclature. It is now the International Code of Nomenclature for algae, fungi, and plants. This terminology seems appropriate in relation to the IPPC, since:
the prokaryotes are entirely excluded
the algae and fungi which are now the concern of IPPC are covered
the plants are now more precisely defined, so that IPPC concern can now extend to macro-plants such as Bryophytes, and algae which are plants (Chlorophyta, Rhodophyta)
concern in principle extends to the algae, fungi and plants which are micro-organisms, although this has at present no practical consequences
this provides a relatively simple formula for practical use, coinciding with that of the International Code.
Organisms covered by this new formula could also be pests of plants, leaving “pathogenic agents” to cover the various bacteria, microfungi, microalgae, protozoa and chromista which are harmful to plants.
In an earlier epoch, living beings were assigned either to the animal or plant kingdoms. This is reflected in the existence of two distinct “Codes of nomenclature”, one for animals and one for plants. This is essentially still the case today, though the titles and texts of the Codes now reflect more precisely their modern scope.
Since the late 19th century, various suggestions have been made to assign organisms to a greater number of kingdoms. In particular, it was perceived that microscopic single-celled organisms could be removed from the Animalia and Plantae and placed in a kingdom Protista, and later that those now known as “prokaryotic” were even more fundamentally different and belonged in a further kingdom Bacteria. Further, it was recognized that Fungi, though still for nomenclatural purposes considered to be plants, formed a quite distinct group within Plantae. The various groups of algae; however, remained as plants.
With the application of electron microscopy, various biochemical characters, a better understanding of the “symbiotic” nature of certain organelles, and most recently nucleic acid sequence comparisons, it became clear that the classification of all organisms, with the exception of the multicellular animals and the non-algal plants, were in need of fundamental rearrangement.
This rearrangement has included the following changes:
The bacteria are now divided into two kingdoms (Bacteria and Archaea), and as prokaryotes are completed separated from the other groups. They now have their own Code of nomenclature. One group of “algae”, formerly the Cyanophyta (blue-green algae,) is now recognized to belong with the bacteria (Cyanobacteria).
The group of microscopic single-celled organisms is now seen to be highly heterogeneous in biochemistry and organelle structure. Two major groups are distinguished – the Protozoa and the Chromista1. These groups also include larger and more complex organisms formerly treated as algae or fungi (see below).
The Fungi are now treated as a separate kingdom, but the group formerly known as Oomycetes is transferred to the kingdom Chromista. The slime-moulds (Myxomycetes) and similar forms like Plasmodiophora, at one time considered to be related to Fungi, also find new places in the Protozoa and Chromista.
The algae disappear as a coherent group. The Chlorophyta2 and the Charophyta remain as plants, together with the Rhodophyta (which may yet, however, move to a kingdom of their own). The Cyanophyta become Cyanobacteria (see above). The Phaeophyta (brown algae) become Chromista. Various groups of microscopic algae become Chromista (diatoms, dinoflagellates) or Protozoa (Euglenozoa). 3
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