Strychnos electri belongs to the genus whose tropical shrubs, trees and vines are famous for producing the deadly toxin strychnine.
The US researchers named it after the Greek word for amber ("elektron") - the fossilised resin of long-dead trees.
Their discovery appears in the journal Nature Plants.
The two flowers were among 500 fossils collected on a 1986 field trip by Professor George Poinar of Oregon State University.
Prof Poinar is a renowned entomologist and most of these specimens were insects. But after nearly 30 years working on the bugs, his eye settled on the flowers.
They were remarkably complete - unlike most plant fossils found in amber, which are usually just fragments.
In 2015, he sent high-resolution photos to Professor Lena Struwe at Rutgers University.
"These flowers looked like they had just fallen from a tree," said Prof Poinar. "I thought they might be Strychnos, and I sent them to Lena because I knew she was an expert in that genus." Read more on bbc.