0.3.3 Classification of Plants
The classification of plants is a difficult theme, both for taxonomists, botanists and homeopaths. Plants are more similar than dissimilar, they all have root, stem, green leaves and flowers.
The classification of plants is called taxonomy. This comes from the Greek taxon, meaning branch. Recently it is often called cladistics, coming from the word clade, meaning group. Another expression is phylogenetics, coming from the Greek word phylum, meaning tribe, and genetics. The word phylogenetics expresses the strong tendency to make a classification that expresses the evolution of the plants. There is a drive to make such classifications that each clade is originating from only one ancestor and includes all descendants from that ancestor. Such a clade is called monophyletic.
There have been several classifications proposed in the 20th century. Examples are those of Bentham, Bessey, Candolle, Cronquist, Dahlgren, Eichler, Engler, Goldberg, Hutchinson, Jussieu, Kubitzki, Melchior, Reveal, Shupinov, Stebbins, Takhtajan, Thorne and Wetstein. Their classifications had a lot in common but were also diverting in many aspects. For instance the Monocotylodons were regarded by most of them as a group or clade.
A group of botanists from different universities came together at the end of the 20th century and formed the Applied Phylogeny Group. They published the first Apg classification in 1998, the second in 2003 and the third in 2009. In this classification DNA analyses were heavily used for the first time in history. Their classification confirmed many aspects of old classifications but also brought to light many new groups and showed that many old clades were inconsistent. Since that time the Apg classification is regarded as the most precise that exists.
Their classification has become quite solid over time. It is quite generally accepted by botanists all over the world but it is not fixed, in the sense that there are still many uncertainties. Most clades are quite well established, being confirmed in studies over and over. But other clades are less certain, or their placement is less certain. Sometimes the placements of a family or order depends on the gene used for analysis. The classification is a work in progress as may be clear from the development from Apg1 to Apg2, to Apg3.
This group of taxonomists comes from several renowned botanical departments all over the world. The grouping is based on the macroscopic and microscopic features, chemistry and especially DNA research. The DNA research has confirmed much of the old classification like those of Cronquist, Dahlgren, Stebbins and Takthajan. But in many parts there have been big changes too.
In this book the Apg3 classification will be used. The classification is frimly built on DNA analysis. Old data such as appearance and chemical analysis is mostly used as confirmation.