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Taxonomy, the branch of science concerned with identifying and classifying species, is not always regarded as the most cutting-edge field of study. But Robert Scotland’s research demonstrates that new, streamlined approaches to the taxonomy of flowering plants can have powerful implications for food research and the conservation of biodiversity.

Ipomoea chondrosepala, a species of the sweet potato family © J.R.I. Wood
Ipomoea chondrosepala, a species of the sweet potato family

You might think that after several centuries of exploration and collection the work of describing and naming the world’s flowering plants would be substantially complete. Of course, some species still remain to be discovered, but surely by now we know essentially what plants there are out there, how much variety there is, and how plants relate to each other in terms of the ‘tree of life’?

There are 3,870 herbaria worldwide containing in excess of 100 million specimens gathered over centuries with the number of herbaria and specimens having doubled since 1960. On the basis of these huge and detailed collections, decisions are made about key issues such as the conservation of biodiversity or the use of ‘wild types’ of plants to enhance the selection of future food crops. So what’s the problem? Why do we still need taxonomy?

The problem with this apparently organised system is that it has been assembled piecemeal, especially with regard to tropical plants. Frequently the same plant will be given different names in different collections; Robert Scotland has conducted research to show that this problem of synonyms affects nearly two thirds of published names. Then there is the issue of misidentification; Scotland’s research also shows that there may be as many as 40,000 completely new species of flowering plants in herbaria, currently wrongly identified or without any name, and waiting to be discovered. This would increase the number of flowering plants known to science by more than 15 per cent – without collecting a single further specimen.

Some of the world’s herbaria can be accessed online through GBIF, the Global Biodiversity Information Facility, which exists to inform ‘better decisions to conserve and sustainably use the biological resources of the planet’. But if the collections are inaccurate, decisions made on their basis will be misguided. In terms of conservation, for example, a study of herbarium specimens may lead to a judgment that a given area of tropical rainforest is not particularly rich in plant species – but a large proportion of its plants may actually be invisible to researchers because they have never been properly identified or collected in sufficient numbers.

In this context, taxonomy starts to look like an essential way of making sense of the muddle. Traditional methods, however, are time consuming and expensive; and the standard approach – comprehensive monographs examining an entire group of plants worldwide – is thorough but unwieldy. Robert Scotland and his colleagues have shown that, using existing methods, there is an average time lag of 35 years between collecting a specimen and accurately identifying and describing it. At this rate, taxonomy would never catch up with the backlog of new species and the explosion in the number of plant collections.

In response, Scotland and John Wood, both at Oxford, in collaboration with others at the Natural History Museum (London) and Royal Botanic Gardens at Edinburgh and Kew, have pioneered a new, rapid, targeted approach to taxonomy that has the capacity to quickly and efficiently uncover new species. The approach is comparable with other areas of science, where the ‘big data’ deluge is increasingly forcing the development of new methods that can deal effectively with very large volumes of information.

Scotland’s approach is to concentrate on large groups of plants that are poorly described, and use ‘broad brush’ methods that avoid getting bogged down in some of the minutiae that can hamper taxonomy (such as differentiating between very similar sub-species of one plant). As well as using sorting and identifying techniques based on examination of plant characteristics, Scotland’s group uses DNA sequencing technology to confirm where plants sit in relation to each other in phylogenetic trees. Crucially, he has established that in the vast majority of cases it is not necessary to sequence an entire plant genome, or even a fraction of it; three key genes (‘barcoding genes’) are often sufficient to differentiate one species from another, and more detailed DNA sequencing is only needed where there is not enough variation between these barcoding genes.

Scotland has recently applied the method – called ‘foundation monographs’ – to a globally important group of plants, the ‘morning glories’ or Ipomoea. This group contains the sweet potatoes, a key food crop in many parts of the world. The results are impressive, revealing a level of diversity within Ipomoea that is far greater than anyone previously suspected. In Bolivia alone, the research identified 102 species of Ipomoea; the previous checklist drawn up in 1958 had identified only 22. Of these 102 species, 18 were completely new – including a plant which is a very close wild relative of cultivated sweet potato. Discoveries like this are very important because of the potential of ‘wild type’ plants to contribute to the breeding of existing food crops. Sweet potatoes in particular flourish on dry, poor soils and could make a significant contribution to food security under future climate change scenarios.

In order to make a breakthrough in our understanding of plant diversity in general and improve our awareness of plants of potential economic value in general we need to know what plants exist and where they grow. Scotland’s method could revolutionise taxonomy and give it the power to tell us about the wealth of flowering plants still lying hidden in collections and in the wild across the world.

Link to Ipomoea(Convolvulaceae) in Bolivia, John R. I. Wood, M. A. Carine, D. Harris, P. Wilkin, B. Williams and R. W. Scotland