Fossil flowers in amber: 15-million-year-old find in China

About 15 million years ago, in a rainforest in what is now southeastern China, drops of tree resin rolled over two tiny flowers and never let go. The resin hardened into amber. The forest around it changed beyond recognition, and this month a team of scientists finally gave the fossil flowers in amber a name.

One of the fossil flowers in amber belongs to a brand new fossil species, Ayenia zhangpuensis, named for Zhangpu County in Fujian province where the amber was found. The second specimen has been assigned informally to Ayenia sp. Both belong to the genus Ayenia in the mallow family, a group of woody climbing vines better known as lianas. The researchers published their findings in the journal Annals of Botany.

Flowers are a hard thing for paleontologists to study. Leaves and wood can survive burial in sediment, but a blossom is mostly water and soft tissue. It rots within days. Amber is one of the few materials that can stop that clock, because resin seals the flower away from air and bacteria before fossilizing into a hard, transparent case.

That rarity is why paleobotanists get excited about a blossom in amber. The Zhangpu deposits hold one of the richest amber biotas in the world, with more than 250 families of spiders, mites, millipedes, and insects preserved across thousands of samples. Insects dominate the record there, though. Reproductive structures like flowers are far less common than insects in any fossil record, and they carry more identifying detail than a leaf, so each new one tells scientists more about what was actually blooming. It has been a busy stretch for botany: researchers also named a tiny devil flower from Thailand a new species this month, while another team sequenced the first European ash pangenome in a push to save the trees. Earlier work on the site traced the amber itself back to resin from tropical Dipterocarpaceae trees, the same family that dominates Southeast Asian rainforests today.

Flowers preserved down to the fine details

The team studied the two flowers with light microscopy and X-ray tomography, which let them examine the delicate internal structures without breaking the amber. According to Gongle Shi of the Nanjing Institute of Geology and Palaeontology, the exceptional preservation allowed the researchers to identify features that are rarely preserved in fossil plants.

What they found was a surprise in its lack of surprise. The flowers look remarkably similar to living Ayenia species, which means the basic floral structure of this lineage has stayed almost unchanged since the Middle Miocene. Fifteen million years of evolution passed, and this flower's design barely budged.

Lianas were already shaping the forest

The bigger payoff is what the flowers say about the forest they came from. Lianas are woody vines that climb into the canopy, where they compete with trees for light and water. In modern rainforests they are a major part of how the whole system is built. The findings show that lianas already played an important role in the vegetation structure of tropical forests during the Middle Miocene.

"The fossils show not only that this plant group existed in Southeast China 15 million years ago," said Eva-Maria Sadowski of the Museum für Naturkunde Berlin. "They also connect a Miocene plant lineage with its living relatives. This provides important insights into how plants evolved and how past ecosystems were composed."

The Zhangpu flora, where the amber comes from, is one of the most important windows scientists have into a tropical ecosystem of the Middle Miocene. At the time, the global climate was warmer than it is today, and the region supported a highly diverse rainforest. Amber from the period preserves plants and animals in exceptional detail, which is why the site keeps producing discoveries.

Reporting on the find, phys.org notes that the study was led by researchers at the Museum für Naturkunde Berlin and the Nanjing Institute of Geology and Palaeontology, with the full paper appearing in Annals of Botany. The museum's own press release says the flowers connect a Miocene plant lineage with its living relatives, and the study authors report that the basic floral structure has remained stable for 15 million years. New species names can sound like bookkeeping, but each one is a timestamp. This one pins a flowering vine to a specific forest on a specific coastline 15 million years ago, and it shows that a small, fragile thing managed to outlast the forest it bloomed in.