A 100-million-year-old piece of amber from mines in the Hukawng Valley of Myanmar (formerly Burma) has revealed the oldest known evidence of sexual reproduction in a flowering plant.
This image shows flowers of Micropetasos burmensis in a 100-million-year-old piece of amber. Image credit: Oregon State University.
The amber contains 18 tiny flowers of a previously unknown Cretaceous plant genus and species, named Micropetasos burmensis.
The perfectly-preserved scene is part of a portrait created when flowering plants were changing the face of the Earth forever, adding beauty, biodiversity and food. It appears identical to the reproduction process that flowering plants (angiosperms) still use today.
The flower cluster is one of the most complete ever found in amber and appeared at a time when many of the flowering plants were still quite small.
Even more remarkable is the microscopic image of pollen tubes growing out of two grains of pollen and penetrating the flower’s stigma, the receptive part of the female reproductive system. This sets the stage for fertilization of the egg and would begin the process of seed formation – had the reproductive act been completed.
“In Cretaceous flowers we’ve never before seen a fossil that shows the pollen tube actually entering the stigma. 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,” said Prof George Poinar, Jr., from the Oregon State University’s College of Science, who is the lead author of a paper published in the Journal of the Botanical Institute of Texas (full paper in .pdf).
The pollen tubes penetrating the stigma on this ancient flower are the only known fossil of this type, showing the process of sexual reproduction in a flowering plant. Image credit: Oregon State University.
“The pollen of these flowers appeared to be sticky, suggesting it was carried by a pollinating insect, and adding further insights into the biodiversity and biology of life in this distant era. At that time much of the plant life was composed of conifers, ferns, mosses, and cycads.”
During the Cretaceous, new lineages of mammals and birds were beginning to appear, along with the flowering plants. But dinosaurs still dominated the Earth.
“The evolution of flowering plants caused an enormous change in the biodiversity of life on Earth, especially in the tropics and subtropics,” Dr Poinar said.
“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.”
“It’s interesting that the mechanisms for reproduction that are still with us today had already been established some 100 million years ago.”
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Poinar GO et al. 2013. Micropetasos, a new genus of angiosperms from mid-Cretaceous Burmese amber. Journal of the Botanical Research Institute of Texas, vol. 7, no. 2
