A cluster of 18 flowers from the Crestaceous Period, contained within a well preserved fossil and discovered in an amber mine in Myanmar, reveal the oldest known evidence of sexual reproduction in a flowering plant. 
One of the flowers, a species now extinct, was reproducing using a process that appears identical to the one used by flowering plants today. Researchers from Oregon State University and Germany published their findings on the 100 million-year old piece of amber in the Journal of the Botanical Institute of Texas.
Microscopic images show pollen tubes growing out of two grains of pollen and penetrating the flower’s stigma. Researchers said the pollen appeared to be sticky, suggesting it was carried by a pollinating insect. The fossils were discovered in amber mines in the Hukawng Valley of Myanmar, formerly Burma. The newly-described genus and species of the flower was named Micropetasos burmensis.
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Source: Oregon State University