The oldest evidence of sexual reproduction in a flowering plant is preserved in a 100-million-year-old piece of amber, according to a report published in the Journal of the Botanical Institute of Texas.

Entombed inside the amber is a cluster of 18 tiny Cretaceous era flowers, one of which is in the process of making new seeds for the next generation. The flowers - from a previously unknown genus and species of now-extinct plant - are in "remarkable" condition, Oregon State University reported Thursday.

"In Cretaceous flowers we've never before seen a fossil that shows the pollen tube actually entering the stigma," said George Poinar, Jr., a professor emeritus in the Department of Integrative Biology at the OSU College of Science. "This is the beauty of amber fossils. They are preserved so rapidly after entering the resin that structures such as pollen grains and tubes can be detected with a microscope."

The amber specimen was discovered in the amber mines in the Hukawng Valley of Myanmar. The species was named Micropetasos burmensis, which makes reference to Myanmar's former name, Burma.

The flowering process preserved in the amber appears to be identical to the reproduction process that angiosperms of flowering plants still use today. Under a microscope, tiny pollen tubes can be seen growing out of two grains of pollen and penetrating the flower's stigma.

Poinar said that the pollen of these flowers appears to be sticky, which suggests it was carried by a pollinating insect.

"New associations between these small flowering plants and various types of insects and other animal life resulted in the successful distribution and evolution of these plants through most of the world today," he said. "It's interesting that the mechanisms for reproduction that are still with us today had already been established some 100 million years ago."