More than one-in-four of all flowering plants are under threat of extinction according to the latest report to confirm the ongoing destruction of much of the natural world by human activity.

As a result, many of nature's most colourful specimens could be lost to the world before scientists even discover them, claims the research, published today in the journal Proceedings of the Royal Society B.

The results reflect similar global studies of other species groups by the International Union for the Conservation of Nature, which estimates that one-in-five of all mammals, nearly one-in-three amphibians and one-in-eight birds are vulnerable to being wiped out completely. Later this year the results of a huge global analysis of all the world's estimated up to 400,000 plants by Royal Botanic Gardens, Kew, is due to be published by the IUCN as part of its ongoing mission to assess the state of all life on Earth.

"[This year] marks the International Year of Biodiversity," said Stuart Pimm of Duke University in North Carolina, USA, one of the authors of the report. "The focus of this celebration has often been on the species we know of, along with discussions on the unprecedented challenge of conserving this biodiversity in the face of threats such as habitat loss. However, by asking just how many species we will lose before they are even discovered, our study has revealed a figure that is truly alarming."

The researchers started by carrying out an independent review of how many flowering plants – which make up most of the plant kingdom – exist. By considering the rate at which new specimens are being described to science, adjusted to reflect the growing number of scientists over the years, and interviewing experts who focus on different groups such as orchids, irises or grasses, the team calculated that on top of the existing "best estimate" of 352,282 flowering plants there are another 10-20%, or 35,000-70,000, which have still to be officially discovered.

The second stage was to assess the level of threats from habitat loss due to clearing land for planting crops or trees, development, or indirect causes such as falling groundwater levels and pollution.

They started with a study published in the journal Endangered Species Research in 2008, which estimated that one-in-five known species were vulnerable to extinction.

However based on the fact that new species – like recent discoveries – are likely to be found in "biodiversity hotspots", where there are huge numbers of endemic species which are not widely distributed around the world, and a high level of habitat loss, they estimated that all so-far-undiscovered flowering plants were also at risk.

"If we take the number of species that are currently known to be threatened, and add to that those that are yet to be discovered, we can estimate that between 27% and 33% of all flowering plants will be threatened with extinction," said David Roberts, one of the co-authors, of the Durrell Institute of Conservation and Ecology at the University of Kent.

The paper adds: "These estimates are based on immediate threat, and do not consider further development of destructive factors - including climate disruption." The paper's third, lead, author was Lucas Joppa of Microsoft Research in Cambridge.

The warning comes as there is growing international recognition of the value of the natural world to humans in providing ecosystem services, from flood protection and medicines to spiritual spaces and enjoyment.

"Plants are the basis for much of life on earth with virtually all other species depending on them; if you get rid of those you get rid of a lot of the things above them," added Roberts.