The State of the World’s Plants

The Kew Royal Botanic Gardens just released the first-ever State of the World’s Plants (SOTWP). This has been making rounds in various news sites, e.g., The Guardian, the Scientific American, etc., after Kew put out its press release. In another opinion piece in the Guardian, Michael McCarthy writes that the report has made “Kew, at a stroke, a global voice for plants.”

I have a bit of beef, however, with Mongabay’s article on it.

First, the article’s title: “How many plant species are there in the world? Scientists now have an answer”.

This conveys a factually wrong message. Scientists have long had an answer. When I was a graduate student, I read Govaerts (2001; Taxon 50: 1085) and Paton et al. (2008; Taxon 57: 602); just last year, there was Pimm and Joppa (2015; Annals of the Missouri Botanical Garden 100: 170). If anything, a “working list” of plant species, enshrined as Target 1 of the Global Strategy for Plant Conservation (GSPC), has often been commented as the best-achieved among all the GSPC targets, having evolved from the International Plant Names Index to the Kew World Checklist to The Plant List today. It was just a matter of narrowing the range of some 250,000-500,000 by extrapolating the degree of synonymy (i.e., redundant names). From what I’ve read, SOTWP simply updated the number using the same methodology of Paton et al. (2008) to arrive at a point estimate of 391,000, which is really still a “working number” of species just as The Plant List is a working list.

In fact, nowhere in the Kew press release did they trumpet this point estimate as a first-ever estimate. Nor did any of the other news sites I cited above. They all simply stated that this is the first report on the state of the plants, which is quite different from being the first to report something. The title of the Mongabay article is an example of the Chinese saying: drawing a snake and adding legs on it.

More lines from the first few paragraphs that could misrepresent what the report has managed to achieve (emphasis mine):

For the first time ever, scientists have assessed the state of all vascular plants in the world…

The report provides — for the first time — baseline information on all vascular plants…

Reading and taking it at face value, you would have thought that the SOTWP team managed to assess the conservation status and provided baseline information of every single plant species in the world, which would be an impossible feat at this point in time. Only 5% of the world’s plant species have been assessed, and again this is a very well-known problem. The “one-in-five” estimate of the proportion of plant species threatened with extinction reported in the SOTWP is simply citing work done by Brummit et al. (PLoS ONE 10: e0135152) creating a Sampled Red List Index for plants, which as the name suggests randomly chooses 7,000 species for conservation assessment to estimate the degree of endangerment in the global plant species pool.

The word all is not just superfluous, but has also innocuously added another meaning, whether or not the writer intended to. Just delete it and it would be much better.

The nuance might be a bit subtle, and admittedly this is not all that damaging a matter, but it is instructive for science communication. It shows perhaps that there is a unconscious tendency to add an unnecessary, inaccurate spin when we are trying to make our science sound more exciting or more urgently requiring the reader’s attention. Mongabay is a respected website for news on tropical conservation, so they need to be extra careful about this to maintain their standing.

Back to the SOTWP, two things caught my attention: something called “Important Plant Areas”, and a claim that some 5,000 plant species are known to be invasive.

I’ve heard of Important Bird Areas by BirdLife International, but not Important Plant Areas (apparently, by Plantlife International), so this is something new. Checking out the interactive map and the database, however, while much of the Indo-Malayan region is shaded, none of the countries (e.g, Indonesia, Malaysia, much less Singapore) have sites listed in the database.

As for the number of “invasive” plant species, it seems to be simply a compilation of various weed/invasive plant databases, all of which have struggled with the problems of defining what “invasive” is, and the level of evidence required for species to be listed.

I can’t help but feel a little disappointed, but oh well, it’s the first report, which tells us that very much more needs to be done.

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