Imagine you’re at work and a cheetah pokes its head through your window.

That’s roughly what Richard McCourt and his colleagues experienced when they came across Lychnothamnus barbatus, a large green alga that was thought to have died out in the Western Hemisphere long before the last of the cheetahs roamed here.

“This means mainly that we don’t know as much about what’s out there as we could,” says McCourt. “Lychnothamnus barbatus’ survival isn’t, per se, ecologically earth-shaking, but it changes our view of what the algal flora of North America is composed of and inspires us to keep hunting for more new finds.”

A paper on the find, featuring mapping and analysis by Academy researcher John D. Hall and lead-authored by Kenneth Karol of the New York Botanical Garden, was published in the American Journal of Botany.

The team took algae samples from 14 lakes in Wisconsin and two in Minnesota between 2012 and 2016 and found the surprising results. The only record of the alga on the western side of the Atlantic Ocean was in Argentinian Cretaceous-era fossils from the same time period as Tyrannosaurus rex, and it had never been seen in North America.

“Almost right away we knew we might be dealing with something previously thought to be extinct because it was clearly different from any other species seen in North America,” McCourt says. “But we had to look at it closely to confirm the identity and also extract the DNA to confirm.”

Much like cheetahs, Lychnothamnus barbatus is relatively rare in the areas it is currently found. A “stonewort” type of alga, it is known to inhabit areas of Europe and Australasia (the area of Australia, New Zealand and Papua New Guinea).

But this species actually grows relatively tall and has a pretty distinct shape to it, raising the question of how it was missed.

“We might not have been missing it — it might be a new invader,” McCourt says.