An extremely rare colony of orchids previously believed to be extinct in Britain has been discovered growing on a City of London rooftop.

The small-flowered tongue orchid, or serapias parviflora, is normally found in the Mediterranean, and hasn't been seen in the UK for over a decade.

But 15 plants have been found on the 11th floor garden of the Japanese Investment Bank Nomura in the City.

It is only the second time the rarity has been recorded in Britain, with a previous colony being found more than 200 miles away Rame Head in Cornwall in 1989.

Unfortunately the Cornish colony was destroyed in 2009, and the species was thought to have gone extinct as a wild plant in the UK.

It's not known for certain how the orchids arrived on the Nomura roof, but Mark Patterson —who manages the roof garden—believes it's plausible they spontaneously colonized naturally without assistance.

He 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 the southerly winds that 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 possible explanation, he said, is that the seeds or young plants could have been brought to the roof in the soil used to create the green roof over a decade ago.

The plants can take many years to mature when growing in dry poor soil conditions, which would explain why we are only now seeing the plants in bloom. However, he explained, this was less likely.

It is not the first time rare orchids have been found on green roofs in the City. Three years ago, Patterson also discovered London's largest colony of green winged orchids growing on the Nomura roof.

Two other green-winged orchids have been found on a rooftop in Carnaby Street, and another plant appeared on a roof in busy Islington.

Wild orchids as rare as these face many threats to their survival, including poor land management, over-grazing, trampling by walkers, and being uprooted and stolen by illegal plant collectors.

The previous known colony in Cornwall had to be kept top secret to protect the plants.

Growing on the roof of a bank in the center of the City, this newly discovered colony plants should be well protected.

Orchid expert Mike Waller, author of Britain's Orchids: A Field Guide to the Orchids of Great Britain and Ireland, said: "To find Britain's second colony of small-flowered tongue orchid is exciting in itself, but to find them on a green roof in the City of London is extraordinary on another level."

He noted that: "This is clear evidence that with patience and dedication, even the most unlikely places can become havens for some our rarest wildlife."

The orchids share the Nomura roof with other rare wildlife including breeding black redstarts—one of the UK's rarest breeding birds.

In 2019, the bank and its charity partner St. Mary's Secret Garden, secured a Bees Needs Award from DEFRA for their work improving the roof environment for bees and other wildlife.

The company has also won numerous London in bloom awards for their roof gardens.

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