About the data

There are more than 380,000 species of plants known to science and even more yet to be discovered. With so many plant species in need of conservation assessment, how do we know if a plant species is threatened?

Some well known species of plants have been intensively studied, but many others, especially in tropical biodiversity hotspots, are only known from the scientific paper where the plant was first described and have never been studied since. Most plant species have no distribution map or population survey and most countries do not have an up-to-date list of their plant species.

Who carried out the assessments?

The monocotyledons and legume groups were assessed by Kew and the pteridophytes were assessed by the Natural History Museum. For each of these groups 1,500 species were selected at random and each assessed against the IUCN categories and criteria.

As there are fewer than 1,500 gymnosperms all species were included, using the existing assessments of the IUCN Conifer and the IUCN Cycad Specialist Groups together with new assessments for the remaining species (Gnetales). We only have preliminary results so far for the sample of 1,500 bryophytes, with a large contribution from the Missouri Botanical Garden. This group is the next to be assessed.

From Darwin to Google: historical records and modern technology

The most comprehensive, easily accessible and reliable information on which to base a conservation assessment for most plant species is the location and range of that species.

Explore the data using our interactive map

The best source of this information is the collection of plant specimens held in the world’s herbaria. A herbarium is a scientific collection of dried, preserved plant specimens that provide verifiable records of the existence of a species at a given time and place. Automated tools for using specimen records to carry out conservation assessments have been developed. Watch our video to find out more about how plants are collected and the role of Kew's Herbarium.

The herbarium collections at Kew contain eight million plant and fungus specimens, and the Natural History Museum contains six million plant specimens, collected by thousands of botanists over hundreds of years, from all over the world.

Together with information about the species from botanical literature, from analysis using Geographical Information Systems (GIS), satellite images in Google Earth and the expert opinion of scientists who study that species or the area of the world where it is found, it is possible to assess a species’ conservation status and assign a Red List category to most species of plants. All assessments carried out for this project are underpinned by accurate and reliable information on where and when a species has been collected.

Example species - hazovola (Dalbergia andapensis). An endangered tree from northeast Madagascar, hazovola is threatened by local deforestation.

Assessing the conservation status of plant species

The IUCN Red List Index provides a rigorous set of criteria to assess the conservation status of a species to see if it is threatened with extinction. Based on these criteria, each species is assigned a category ranging from Critically Endangered (very close to extinction) to Least Concern (under no or very little risk of extinction), or Data Deficient if there is not enough information to reliably assess the status. Read about the IUCN Red List Index categories and criteria in more detail.

To assess the conservation status of a plant species and see if it is threatened with extinction, it must be assessed according to this rigorous set of criteria, after which it is assigned a category. By assessing a representative, random sample of species in a group of organisms, we get a picture of the overall conservation status of that group, and doing this regularly shows the trend in status over time.

Explore the state of the world's plant life using Kew's interactive map.

The Sampled Red List Index - plants compared with other groups.

Why is it called a 'Sampled Red List Index'?

Plant groups are relatively poorly known compared to animal groups such as birds and mammals. This is because there are many more species of plants than there are birds and mammals, but there are also more scientific experts for birds and mammals too.

Every species of bird, mammal, amphibian and coral has been assessed, but for much larger groups, such as plants and insects, this is not possible. Instead a representative sample of species has been selected, so for plants we produced a 'Sampled Red List Index'.

By assessing a randomly selected sample of plant species we get a picture of the overall threat status for each major plant group, without having to assess every species. Simulation modelling from the complete IUCN Red List assessments of birds and amphibians confirmed that 1,500 species for each group of plants would provide a representative view of plants overall.

In this research project, 7,000 plant species drawn from the five major groups of plants were included in the study: bryophytes (mosses and liverworts), pteridophytes (these are land plants, such as ferns, that produce neither flowers nor seeds and reproduce via spores), gymnosperms (such as conifers and cycads), monocotyledons (one of the major groups of flowering plants including orchids and the economically important grass and palm families) and legumes (the pea and bean family), as representative of the other flowering plants.

Both common and rare species were assessed in order to give an accurate picture of how plants are faring around the world.

Plant groups explained.

Plants in comparison with other organisms

The IUCN Sampled Red List Index for Plants has a value scaled between 1 and 0, where a value of 1 would indicate that no species in the world was threatened, whereas a value of zero would indicate that every species in the world had gone extinct. The Sampled Red List Index value for Plants is [0.86], which shows that:

Plants are more threatened than birds.
Plants are as threatened as mammals.
Plants are currently not as threatened as amphibians or corals.

In the future, the sample of plants will be assessed again to see how the threat status of each plant species has changed. The next point on the graph could show that the situation is improving (the line goes up) or getting worse (the line goes down). The future of plants depends on the conservation actions taken in the next few years.

Plants under pressure brochure (pdf)