A super-rare Amazonian cactus is set to flower for what is thought to be the first time ever in the UK - for 12 hours only. The tropical Moonflower, or Selenicereus wittii, is usually exclusive to the floodplain rainforests of the Amazon Basin in South America. However, Cambridge University Botanical Gardens (CUBG) has been home to one of these rare and exotic cactus plants since 2015. And now, for the first time, a bud has grown from the bizarre-looking plant - and staff at the Botanical Gardens are excitedly watching to see it flower, which could happen as soon as today (Tues). The strange-looking bud, which measures an impressive 27cm, will bloom overnight into white, nocturnal flowers - which will close up again just 12 hours later, by the following sunrise. And the bud itself, which is covered with tufts of 'hair' whilst closed, appears as if it is growing straight out of the trunk of another tree in the CUBG Tropical Glasshouse. But in reality, the Moonflower is an epiphyte - meaning it relies on another plant as an anchor point. At CUBG, the cactus' strange, flattened, leaf-like stem has wound its way around a Water Chestnut tree - with the bud growing out of the stem at a point where the light hits it. Alex Summers, Glasshouse Supervisor at CUBG, who is responsible for growing and nurturing the Moonflower, said: "I'm so intrigued and excited to see and share this most unusual flowering. "It's very rare to have this plant in our collection and we believe this is the first time the Moonflower has flowered in the UK. "I noticed the flattened stems, or pads, which swirl around the trunk of our Water Chestnut had sent out a flowerbud in late November. "This was a lucky spot as it's almost 12 feet up in the air and could have so easily been missed. "But it has only recently increased radically in size - which means a flowering is imminent." When the plant eventually flowers, the process begins by the breaking bud emitting a sweet-smelling fragrance just as it begins to open, and throughout its flowering. This sweet smell attracts the night-flying hawkmoth - which is believed to be the only insect able to pollinate the Moonflower, due to their extremely long tongues. Alex said: "The flower has its nectar right at the base of the floral tube which means it can only be pollinated by an insect with a long tongue or proboscis. "This is believed to be only one or two species of hawkmoth. Once it has flowered and hopefully successfully pollinated, it then dies a few hours later, emitting a rancid smell." Two hours after flowering begins, the plant changes its scent to something far less pleasant, and the flowering is over by sunrise. But Alex hopes this will not be the only time that the Moonflower flowers at CUBG - as he is planning to hand-pollinate it, with the hope of producing seed. He said: "We expect it to flower like this most years from now on." And Alex added: "Other than being a highly rare and unusual event to witness, I also love the story about how this elusive flower came to our attention. "This is thanks to an intrepid British female environmentalist and Botanical artist Margaret Mee. "She first saw the Moonflower in the Amazon in 1972 and then went back in her 70s to paint it in 1988." Whilst Alex will not be producing his own painting of the tropical plant in bloom, he will be capturing the historic event on camera. Alex and his Glasshouse assistant, Barbara, are tending to the flower through the night, to ensure they don't miss the big event. And any other botanist enthusiasts eager to catch the rare flowering can watch it via a live-stream on the CUBG website: https://www.botanic.cam.ac.uk/moonflower/.