York groundsel, Senecio eboracensis, is a natural hybrid unique to York, England and was only discovered in 1979 growing on derelict land and railway sidings there. Authorities immediately set about eradicating the "weed" and succeeded in doing so by 1991. Only seeds remained, stashed in the Millennium Seed Bank, and they allowed the otherwise extinct plant to be re-established. The Guardian reports that it's the first successful example in Britain of de-extinction and validates the general credibility of seed banks.
Andrew Shaw of the Rare British Plants Nursery had a vision to bring the species back to life, but when tests were carried out on some privately held seeds very few germinated successfully.
So Natural England, the government's conservation watchdog, quickly authorised a de-extinction attempt via its species recovery programme, which has funded the revival of the most threatened native species for 30 years.
"The Millennium Seed Bank said the seed was getting near the end of its lifespan and so we thought we would only have one more chance of resurrecting it," said Alex Prendergast, a vascular plant senior specialist for Natural England.
Sounds like they were getting desperate, too: previous attempts failed and they were down to a few grams of seeds. Next up, velociraptors!