On Monday, the botanist and her collaborator, Oregon State University's George O. Poinar Jr., who found the two amber fossils, announced that the plants they contained represented a new species, Strychnos electri. For Agatha Christie fans, this is a distant cousin of the plant that contains the poison substance strychnine.
Struwe had identified dozens of other new species before, usually plants that were already housed in museum collections. None was from modern field expeditions like this one, and none was anywhere near so old. Animal bones are one thing, but for a flower to be preserved for eons, the odds have to line up just right.
Yet there they were, two ancient specimens looking much like modern cousins on the woody vines known as lianas, she said.
"It is pretty amazing that they have survived so long and they look so incredibly perfect," Struwe said. "They look like something that fell off one of these lianas yesterday."
This is a regular detective story, in which Struwe visited the historic collection at Philadelphia's Academy of Natural Sciences of Drexel University, reviewing scores of known species to determine that the ancient petals trapped in amber were, in fact, new.
She also looked at specimens at the New York Botanical Garden in the Bronx and at other species described in the scientific literature, comparing the amber-trapped flowers with 200 known species of Strychnos.
Among the key differences that set the new find apart from some of its close cousins: its flower petals have hairs on the outside, but not inside, she said. The findings were published in the journal Nature Plants.
Scientists at the Academy of Natural Sciences say the research illustrates the value of museum collections such as theirs, which contains an estimated 1.5 million botany specimens, some dating back to the 1700s.
"There's so much more that you could see from a specimen than you could ever see from a photograph or a drawing," said Tatyana Livshultz, the academy's assistant curator of botany.
Such specimens are useful not only for classifying new species; they also enable researchers to study broad environmental trends such as climate change.
Each of the dried, preserved plants at the academy is carefully labeled with a location and date, so scientists can tell, for example, if a certain plant now flowers earlier than in previous years due to warmer temperatures, Livshultz said.
"It's really the most granular documentation we have of species occurrence through space and time," she said.
Struwe and Poinar, the authors of the paper describing the new Strychnos species, are among the small number of scientists who have drawn notice in the popular realm.
Struwe blogs at www.botanicalaccuracy.com, gently pointing out mistaken identifications of plants in popular culture.
Among her past targets was an ad for Apple's iPhone 4S, in which the phone's internal assistant, Siri, was asked what poison oak looked like. But the phone incorrectly displayed an image of poison ivy, she said.
Meanwhile, Poinar's work on insects trapped in amber inspired author Michael Crichton to write the Jurassic Park books. (And yes, Poinar often gets the question of whether we could really make dinosaurs from DNA extracted from bloodsucking insects trapped in amber. Answer: Leave it to Hollywood.)
Poinar found the amber containing the flowers in 1986 in the Dominican Republic, and found so many other samples that he only recently had the time to tackle the mystery flowers.
Poinar identified Struwe as someone who had studied similar plants in the past, and sent off an email.
The 200 or so members of Strychnos, including the new one, are part of a much larger plant group called the asterids, which includes mint, potato plants, and olive trees.
The new find suggests that tropical forests were rich in diversity millions of years before humans came along, Struwe said.
"There was nobody back then that could pick them up and look at them," she said. "Now we do this based on these remnants, these time capsules from these ancient tropical forests."