Magic mushrooms sprout in Kensington Gardens

They resemble large glowing mushrooms and have sprung up beside the Serpentine Gallery over the past six weeks. These 5.5-metre tall fabric parasols, designed by architect Zaha Hadid, will create shelter for guests at the gallery's annual summer party on 11 July.

The illuminated pieces were commissioned at the eleventh hour when it became clear the gallery's traditional summer pavilion - this year designed by artist Olafur Eliasson, the man behind the giant sun installation at Tate Modern - was not going to be ready in time for the event.

Eliasson's pavilion will now open in August and stay up to coincide with the increasingly important Frieze Art Fair in October.

Meanwhile Ms Hadid, a trustee of the gallery and one of the world's best-known architects, stepped in. She will host this evening's party with US actor Dennis Hopper.

The guest list includes Nicolas Cage, Kim Cattrall, Danny Huston, Rhys Ifans, Rod Stewart and Kevin Spacey. Among the artists expected to attend are Damien Hirst, Antony Gormley and Tracey Emin.

Ms Hadid said she and colleague Patrik Schumacher were delighted to be able to help when approached six weeks ago. "We always enjoy doing this sort of thing," she said. "It's fun."

Ms Hadid is also being honoured this summer with an exhibition at the Design Museum. Deyan Sudjic, its director, said that of all the architects of her generation in London, she was the one who had made "the most exciting career".

Although acclaimed around the world, the Baghdad-born, London-trained architect is only now designing her first buildings for her adopted home city. They include the swimming pool for the Olympic Games and a new gallery in Hoxton Square.