The two 20-30 million-year-old fossil flowers found perfectly preserved in a piece of amber came from the dark side of the asterid family - they belong to the genus Strychnos, which ultimately gave rise to some of the world's most famous poisons, including strychnine and curare.
Poisons that would later find their way into blow-gun weapons, rat control, Sherlock Holmes stories and the movie "Psycho" appear to have had some of their ancestral and biological roots in the prehistoric jungles of what is now the Dominican Republic, researchers said.
"Specimens such as this are what give us insights into the ecology of ecosystems in the distant past," Poinar said.
"It shows that the asterids, which later gave humans all types of foods and other products, were already evolving many millions of years ago," he said.
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Asterids, the researchers said, are among Earth's most important and diverse plants, with 10 orders, 98 families, and about 80,000 species. They represent about one-third of all the Earth's diversity of angiosperms, or flowering plants.
"Species of the genus Strychnos are almost all toxic in some way," Poinar said.
"Each plant has its own alkaloids with varying effects. Some are more toxic than others, and it may be that they were successful because their poisons offered some defence against herbivores.
"Today some of these toxins have been shown to possess useful and even medicinal properties," said Poinar.
As natural poisons that humans came to understand and use, two extracts from plants in the Strychnos genus ultimately became famous - strychnine and curare.
They are still being studied for medicinal properties, such as for the treatment of parasitic worm infections and even as drugs to treat malaria, researchers said.
The discovery of these two fossil flowers, researchers said, suggests that many other related plant families could have evolved in the Late Cretaceous in tropical forests.
The study was published in the journal Nature Plants.