World’s largest amber flower re-examined

World’s largest amber flower re-examined

Symplocos kowalewskii in amber. © Carola Radke/ Museum of Natural History Berlin

The largest known flower enclosed in amber measures 2.8 centimeters and is around 34 to 38 million years old - and it apparently belongs to a different plant genus than previously thought. This shows an analysis of the pollen of the extraordinary specimen. While the flower was classified as a false camellia when it was first described in 1872, the current study uses scanning electron micrographs to show that it belongs to the genus Symplocos. The new findings provide insights into the flora of the Eocene and enable conclusions to be drawn about the climate of the past.

Around 34 to 38 million years ago, in the late Eocene, the so-called amber forest was located on the Baltic Sea. The resin of the trees of this primeval forest is found today as Baltic amber. One of the largest deposits in the world is located in Kaliningrad in today's Russia. Some of the amber contains tiny inclusions of animals and plants from the time when the resin dripped from the trees. As if in a time capsule, the enclosed animal and plant parts were preserved in the amber for millions of years - and can today give researchers insights into the fauna and flora of the time.

Detailed flower

One of the most extraordinary finds from the amber deposit in Kaliningrad is a 2.8 centimeter flower that has been preserved in three dimensions and with fine details in the amber. Compared to inclusions from small arthropods, such plant inclusions are rare. "Only one to three percent of all inclusions from late Eocene Baltic amber are of botanical origin," report Eva-Maria Sadowski from the Berlin Museum of Natural History and Christa-Charlotte Hofmann from the University of Vienna. "However, the botanical inclusions present are valuable for understanding the evolution of plant stems, their paleobiogeographical history, and the area of ​​origin of the amber, including habitats, plant diversity, and paleoclimate."

With a diameter of almost three centimeters, the flower from Kaliningrad is around three times the size of most other known flower inclusions, making it the largest flower in the world preserved in amber. Apart from its size, it has another special feature: numerous pollen have escaped from its stamens and have also been preserved in the amber. "Finding such a large flower in amber, which also releases its pollen at the exact moment it was embedded in the resin, is very unusual," says Sadowski.

Primeval pollen under the electron microscope

The flower was discovered and first described in 1872. At that time, scientists assumed that it was a false camellia (Stewartia) and therefore gave it the name Stewartia kowalewskii. Later, however, doubts arose about this assignment. Sadowski and Hofmann have now reanalyzed the flower. In order to obtain as detailed information as possible, they carefully scraped out individual pollen from the amber with a scalpel and examined them under the scanning electron microscope. "Only under extremely high magnification can morphological details be recognized on the pollen grains, which are only a few micrometers in size," explains Hofmann.

The researchers compared the structure of the pollen grains and the shape of the stamens and petals of the flower with other modern and extinct plants. The result: Contrary to what was previously assumed, the flower does not belong to the false camellias but to the genus Sympolocos from the Symplocaceae family. Also known as "sweetleaf" in English-speaking countries, this family includes shrubs and small trees. Instead of Stewartia kawalewskii, the flower now bears the scientific name Symplocos kowalewskii.

Insights into the flora of the Eocene

"This fossil is the first record of Symplocaceae from Baltic amber," the authors write. Today, these plants are only found in tropical and subtropical areas in East and Southeast Asia. In the late Eocene 34 to 38 million years ago, however, Europe also offered them suitable living conditions. At that time, the climate on the Baltic Sea coast was warmer and rainier than today, allowing a diverse ecosystem of coastal swamps, moors and mixed forests to develop.

"Our new findings about this uniquely beautiful flower inclusion are an additional piece of the puzzle that will help us to further decode the flora of the Baltic Amber Forest and thus to draw conclusions about the climate of past times," says Sadowski. "Only with such insights can we gain deeper insights into the forests of the earth's history and understand their change over time."

Source: Eva-Maria Sadowski Museum für Naturkunde, Berlin) et al., Scientific Reports, doi: 10.1038/s41598-022-24549-z

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