The Walled Garden has been used to group plants together in one way or another ever since the Garden's creation. During the 1600s, as a Physic Garden, plants were classified based on their medicinal properties. Later, during the mid 1800s, the plants were arranged by geographical origin as more material became available from abroad.
The current arrangement of beds were laid out in 1884 by Professor Isaac Bayley Balfour. This time the plants were grouped into botanical families following the Bentham and Hooker system of plant classification based on morphological characters, such as the number of floral parts.
All of these previous systems of classification are considered artificial. Today we have a much clearer understanding of plant classification.When grouping plants together we now attempt to reflect evolutionary relationships.
The work of the Angiosperm Phylogeny Group (APG), led by Professor Mark Chase of the Royal Botanic Gardens Kew, has introduced molecular data from the study of plant DNA to construct a more accurate system of plant classification. Non-flowering plants like the mosses, ferns and conifers are not part of this system.
All the species in a plant family now form a natural group, having descended from a common ancestor at sometime in the past. The advantage of this new system is that we can accurately identify which plants are related to one another. One benefit of this is the search for new medicines. If a particular plant is known to produce a medically important chemical, the chances are that the relatives of such a plant will also yield similar chemicals. In essence an accurate, natural system of classification becomes predictive.
The Botanic Garden was among the first to adopt this new classification system within the plant collections.
The APG classification is used in the teaching of plant systematics and taxonomy at the University of Oxford. The beds are also used to communicate the importance of plant classification to all users of the Botanic Garden. Visitors can now walk through flowering plant evolution, starting with plant families that were first to diverge from the evolutionary tree, through to those that formed new groups at more recent periods in geological history.