Much of the Walled Garden at the Botanic Garden is made up of rectangular botanical family borders. These were first laid out in 1884 by Sir Isaac Bayley Balfour using the Bentham and Hooker system of classifying plants, which he had adapted to reflect his own ideas. Throughout the twentieth century this piece of botanical history was preserved within our ancient walls and was used to teach undergraduate students how plants are botanically related. However plant classification has moved on apace over the years.

Following the work carried out by the Angiosperm Phylogeny Group (APG), led by Dr Mark Chase of the Royal Botanic Gardens, Kew, molecular data is now thought to support a more appropriate system for classifying flowering plants (non-flowering plants like conifers, ferns and mosses are not a part of this classification system). It is being used in the teaching of taxonomy at Oxford University and we are one of the first botanic gardens to use this system within our botanical family borders.

The family borders are a fascinating way of discovering which plants are related to each other and which botanical families are important in supplying us with food, fibres and medicines. But they are also a great place to discover new plants to grow in our own gardens. As gardeners we have tried to plant up each of the borders combining botanical accuracy with aesthetics.

What makes one plant “related” to another?

Traditionally, plants were grouped into species, genera and families. Plants of the same species will look more or less identical to one another; for instance, all stinging nettles in our countryside look the same, they are the same species and they can pollinate each other to produce seed. Plants in the same genera, look similar to one another, but different enough to have a different name. The stinging nettle we are familiar with has a New Zealand relative in the same genus that becomes a small tree and its sting can cause illness or death! Both are in the genus Urtica, because of their basic similarities, but are different species owing to their greater physical differences.

Finally we have families. A family of plants is a higher order of classification, and includes all the different genera that still have enough basic similarities to suggest that they all evolved from a common ancestor.

The New Order

However plants can be tricky, and some plants fooled the early experts by having characteristics, which seemed to place them in a particular family. The classification system we have adopted at the Garden (the APG system) has taken all the traditional information and added molecular data gleaned from DNA. This system has solved some mysteries, which have plagued systematists (people who spend their lives studying such things) and shed light on new relationships not before understood. Now you can stroll along an evolutionary path from the least specialised of the flowering plants through to the most specialised, as you walk within the Walled Garden. This has meant that our Botanic Garden is now a living library rather than a preserved museum.