Generations of botanists had tramped unwittingly past the diminutive blue flower without noticing it. But worldwide fame now beckons for a previously unidentified iris that flowers for just two weeks a year in a field of daisies in the Western Cape.

South African plant experts who finally spotted the iris last year have launched an online auction of the naming rights to the new species. It will culminate in a gala dinner in Cape Town on 31 March, aimed at highlighting the fragile biodiversity of the tip of Africa and raising money to save plucky indigenous plants like these.

"This iris was already endangered when it was found,'' said Amy Goldblatt, a fundraiser for the World Wide Fund for Nature (WWF) Table Mountain campaign. "Some species, such as this iris, have a tiny radius. If you plough a field the size of a rugby pitch, they can be gone from the planet forever.''

Koos Claasens spotted the pale blue flower when he bought his farm at Jacobsbaai, on the Saldanha Peninsula, 140 km north Cape Town in 1995. "It only flowers for two weeks in September and it is well hidden by the daisies. When I saw it, I did not realise it was undiscovered. Then a PhD student came here to do a species count. We squared off an area of 10 x 10 metres and found 91 different species in that small plot. She made enquiries and eventually confirmed the iris was new.''

Claasens's Atlantic-facing farmland has been identified by the Table Mountain fund for one of 28 "corridors'' it wants to protect from the ravages of climate change and real estate development. The 6bn rand (£53m) campaign aims to purchase some land and, in other cases, finance stewardship schemes with landowners.

Goldblatt said the Western Cape was one of six "floral kingdoms'' in the world identified by the United Nations Educational, Scientific and Cultural Organisation (Unesco). "Ours is the smallest floral kingdom but the richest. About 6,200 of its 9,000 species grow nowhere else. Table Mountain alone supports around 2,200 plant species which is more than the entire United Kingdom,'' she said.

Iris bulbs were among the first southern African plants taken to Europe in the 17th century. Sponsored by royal families, botanists engaged in a veritable iris race to bring ever more beautiful species to European greenhouses.

Goldblatt was not able to predict how much the auction, which is being run by Strauss & Co, would raise. But she already had in mind a favoured highest-bidder. "We cannot sell the rights to an oil or gas company – that would be against WWF rules. But this would be a beautiful gift from Prince William to Kate Middleton,'' she enthused.