An aerial image of the Amazon rainforest, showing the river meandering through green forests

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How to count every plant in the Amazon rainforest

Scientists have for the first time a clear baseline figure for the number of plant species that grow in the vast lowland rainforests of the Amazon.

By painstakingly cross-checking data from botanical collections around the globe, the international team found that 14,003 seed plants, which include flowering plants and the palm-like cycads, have been recorded as growing in the forests.

The scientists discovered that fewer than half (just 6,797) of the plant species are trees, a number lower than suggested in previously published work. But herbs, shrubs and epiphytes - plants that grow on other plants - were more diverse than anticipated, showing they have often been overlooked in studies of tropical diversity.

Dr Sandra Knapp, head of the Museum's Algae, Fungi and Plants Division, contributed to the project. She says, 'By establishing a verified baseline for Amazonian plants, we have solid basis for conservation, but also for studies of the evolution and ecology of these extraordinary and wonderful forests.'

A coloured map showing the number of plant species in regions with Amazonian rainforests, overlaid on an aerial picture of the Amazon

The number of plant species by region in the Amazonian rainforests. For each region, the top number is the total number of species and the bottom is the number of tree species. (The photograph in the background shows the Amazon forest in Serra da Mocidade National Park, Brazil © Ricardo Azoury)

Estimating biodiversity

The Amazon basin is one of Earth's hotspots of biodiversity. Just how many plants live there has been fiercely debated, with estimates for flowering plants ranging from the tens to hundreds of thousands.

The new study looks at the records of actual plant specimens collected by botanists over centuries of Amazon exploration. These are held in museums and herbariums scattered across the globe.

The team have taken advantage of the digitisation boom and investment by governments in creating lists of the plants of Colombia and Brazil. They have compiled a master list by using databases worldwide and the expertise of botanists who work with Amazonian flora.

An image of the Parkia pendula plant, showing its round red flowers that hang downwards

Parkia pendula is a flowering plant in the pea family, the Leguminosae. This is the largest plant family recorded in the Amazon, with almost 1,400 members. © Mauricio Mercadante licensed under CC BY-NC-ND 2.0 via flickr

Counting carefully

While having access to all these records is useful, they must be used with care, cautions Dr Knapp. 'One of the great things about having lots of digital data available is that you can amalgamate and aggregate it very easily. But it's important to verify the data and make sure that nothing is duplicated or has been put in by error.'

The team relied on the work of taxonomic specialists – who are experts in the identification and classification of organisms – to carefully comb through the assembled databases and root out errors.

'This study highlights the importance of institutions like the Museum which have both extensive collections and taxonomic experts who can study them,' says Dr Knapp. 'They provide the solid base on which to base conservation and sustainable use.'

An image of the rainforest looking at the plant growth in-between the canopy and forest floor, showing plants with large leaves in the dim light conditions

The understory of the rainforest, between the canopy and the forest floor, is dim, hot and humid

Continued exploration

Dr Domingos Cardoso of the Federal University in Salvador, Brazil, led the study with Dr Tiina Särkinen of the Royal Botanic Garden, Edinburgh.

'Publication of this list does not mean that the Amazonian flora is completely known,' says Dr Cardoso. 'Many new plant species are discovered each year, both in the field and in museum and herbarium collections – and much of the vast Amazon area still remains poorly or completely unexplored.'

The team's cleaned list will be published open access and made available for others to use in their studies of the Amazon, says Dr Knapp. 'It's important to share as people think of ways to use data that we would never have thought of.

'Locked in a building it doesn't do anyone any good, but out in the open it can.'

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