Botanists had long believed the accepted number of flowering plant species to be an overestimate, but few are likely to have guessed the scale of the miscalculation. New research suggests that at least 600,000 flowering plant names – more than half – are synonyms, or duplicate names.

Many plant species end up with more than one name, a particularly extreme example being the tomato (Solanum lycopersicum), which has about 800 aliases. Alan Paton of the Royal Botanic Gardens, Kew in London, part of the team working to tackle synonymy, says the problem occurs across the plant kingdom. “There are generally about two and a half synonymous names for every accepted name,” he says, adding that widespread and economically important species, such as the tomato, “tend to have more synonyms”.

Historically, the obscure nature of botanical literature has made it difficult for researchers to access all the existing accounts of the groups they are studying, where they might have discovered that the ‘new’ species they had stumbled on, named and described was actually old hat.

Even in more recent times, information about plant names is spread around several databases in different parts of the world, and the data have never been gathered in one place before.

Now, after nearly three years of working to weed out synonymy in some of the largest and most comprehensive of these databases, researchers at Missouri Botanical Garden in St Louis and Kew have produced ‘The Plant List’, a definitive working list of all plant species.

A survey of plant names on this scale has never been undertaken before because of the huge amount of data involved, but now the use of an automated, rule-based system has provided a breakthrough.

“We’ve been merging these databases, but there are conflicts,” says Paton. “You have to decide which source you prefer. We take global sources in preference to regional ones, and later sources over earlier ones.”

The researchers have downgraded the likely number of flowering plant species from previous estimates of around one million to about 400,000, suggesting that at least 600,000 accepted species names are invalid.

The list is currently a first-draft, and work remains to be done before it is truly definitive. “There are other datasets out there that we’d like to get hold of and add to this global dataset,” says Paton.

The team hopes their final list will be published and made widely available to researchers by the end of 2010. “We want to provide something useful quickly because at the moment there is nothing which is globally comprehensive and provides synonyms,” says Paton. “It won’t be perfect, but it will be the best thing there is in one place.”

The creation of such a list was the primary target of the Global Strategy for Plant Conservation, first proposed in 1999 and adopted by 139 nations as part of the Convention on Biological Diversity in 2002.

The current draft of ‘The Plant List’ has already been used to help choose which plant species will be included in the Red List Index for Plants – a global analysis of extinction risk.

Image: Solanum lycopersicum flower. Photo by André Karwath via Wikimedia Commons under Creative Commons