Serapias parviflora, also known as small-flowered tongue orchid, was found growing in the 11th-floor rooftop garden of the Japanese investment bank Nomura. It is usually found in the Mediterranean basin and the Atlantic coast of France, Spain and Portugal. It is only the second time the species has been found in the UK. The previous colony was found in Rame Head, Cornwall, in 1989, but was destroyed in 2009 as a result of land mismanagement. The 15-plant colony in London is believed to be the only one in the UK. The plants grow to about 30cm and typically have between three and 12 tiny flowers, which are usually orange. Other orchids have made their home at Nomura. London’s largest colony of green-winged orchids, usually found in Europe and the Middle East, was found in its rooftop garden three years ago. Mark Patterson, who manages the garden, discovered the latest orchids during a monthly survey. How the orchids arrived is not known, but Patterson said: “Orchid seeds are incredibly small and can travel great distances by wind. The plants could have originated on the continent and been brought over the Channel on southerly winds which frequently bring Saharan dust deposits to the capital. “Once settled on the Nomura roof the seeds would have formed a symbiosis with a mycorrhizal fungus enabling them to germinate and grow. While possible, the odds are astronomical.” Another explanation, he said, is that the seeds were brought to the roof in the soil used to create the garden more than a decade ago. The plants can take many years to mature when growing in dry and arid soil conditions. Mike Waller, an ecologist and co-author of Britain’s Orchids, said: “To find Britain’s second colony of small-flowered tongue orchids is exciting in itself, but to find them on a green roof in the City of London is extraordinary. “This is clear evidence that with patience and dedication, even the most unlikely places can become havens for some of our rarest wildlife.” Despite jubilation at the discovery, some botanists are concerned about flower species arriving from warmer climates as temperatures continue to rise. Mark Spencer, the honorary botany curator for the Linnean Society of London, said: “While on one hand this is a very interesting event, there is a deeply concerning undercurrent, namely climate change. “This is one of many Mediterranean ecosystem plants that are colonising the UK and expanding their range. The extent of these changes are very considerable and they are yet another example of the natural world responding rapidly to these pressures while we remain largely oblivious.”