The slimy-fruited stonewort was last seen in Great Britain in 1959.
That was until Suffolk Wildlife Trust farm conservation adviser Juliet Hawkins identified the distinctive pond plant - Nitella capillaris - while surveying farmland ponds in the east of the county last month.
Also known as charophytes, stoneworts thrive in clean water and provide underwater shelter and breeding opportunities for aquatic invertebrates, snails and amphibians.
Following her discovery, Ms Hawkins e-mailed photographs late the same night to the national charophyte recorder, Nick Stewart, who in turn contacted experts in Germany and The Netherlands. By the morning, she had Europe-wide confirmation her find was indeed a species thought to be extinct in the UK.
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Coup
Further excitement came when two other very rare stoneworts were found in nearby ponds - the nationally scarce clustered stonewort and the endangered tassel stonewort.
"For a botanist, this is quite a coup - to have three rare stoneworts in such a small area," said Ms Hawkins.
"I have surveyed around 1,500 ponds since 2003 and as soon as I saw the slimy-fruited stonewort, I knew I'd never seen it before. The farmer we've been working with has been funding the restoration of the ponds along with his Countryside Stewardship scheme and is absolutely thrilled. We will work with him to look after it into the future."
Ms Hawkins said samples have been sent to the National History Museum in London for analysis. She is linking their appearance to a farmland pond restoration project she has been involved with, which has seen ponds cleared of debris, creating the conditions for stonewort spores to re-activate, after having been lying dormant in the pond bed for decades.
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Germinate
"Historically, farmers kept their ponds clean as a water source for livestock," she explained.
"They periodically cleaned their ponds and spread the leaf matter on the field which added to soil humus in the heavy clay. Trees and shrubs were coppiced to ensure good access to the water for livestock and this would have allowed more sunlight in.
"Stoneworts would have had good periodic opportunities to germinate after a pond cleaning, fruit and set their spores and lie low for another 10 years or so."
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