A collection of pressed flowers taken from the hillsides of Bologna 500 years ago is unlocking knowledge about how the climate crisis and human migration is changing landscapes in northern Italy.
Picked between 1551 and 1586 by the Renaissance naturalist Ulisse Aldrovandi, the 5,000 delicately cut and dried plants form one of the richest collections of its time.
Aldrovandi’s original purpose was to identify plant species and understand which could be used for pharmaceutical purposes. Nearly half a millennia later, his carefully pressed specimens are helping botanists document the enormous changes that have taken place in the surrounding landscapes, according to new research published by the Royal Society.
During Aldrovandi’s time, Bologna’s hills were rich in species that are threatened or have even disappeared today, such as motherwort, which was used for medicinal purposes and is now likely extinct in the region. The total number of the species has increased since 1500s, but the quality of the flora has decreased, with many rarer species declining, researchers said. The Italian population increased by 560% during the study period.
Aldrovandi’s herbarium is made up of 15 books, each containing up to 580 specimens glued to sheets. The collection includes notes on species’ frequency, abundance, ecology, local names and uses in folk medicine. Researchers believe it is the oldest example of a herbarium containing such detailed notes. “From a historical and scientific perspective”, the researchers write, “the importance of this herbarium is inestimable.”
“Aldrovandi’s herbarium preserves the memory of the first signs of a radical transformation of the European flora and habitats,” the paper says.
One part of that transformation is the huge influx of non-native species. At the time the collection was formed, just 4% of flowers were American species, which were almost exclusively cultivated in private or botanical gardens. Plants such as sweet pepper and courgettes were imported thanks to early exploration in Central and South America. Since then, there has been a 1,000% increase in non-native flowers from the Americas, which illustrates the growing importance of American-European trade routes from the Renaissance onwards.
“We would never expect to see such a strong difference,” said the lead researcher, Dr Fabrizio Buldrini from the University of Bologna. “These increases are frightening, in some respects, because they are the unequivocal sign of profound human impact.”
Buldrini’s team compared flora collected by Aldrovandi with collections made by Girolamo Cocconi (1883) and Emilia-Romagna (1965-2021). They looked at the plains area surrounding the River Po and its tributaries, where they could make comparisons across the datasets.
The data also shows the effects of the “little ice age”, which extended through to the mid-1800s. High mountain species such as the silver cranesbill are typically found more than 1,700 metres above sea level, but Cocconi found it at 800 metres above sea level. The mountain buttercup is now only found above 1,000 metres, but during the “little ice age” it was found at 300 metres.
Aldrovandi also helped create the city’s botanical garden, one of the earliest in Europe. A number of important collections were made around his time and in the centuries after, with Bologna becoming a “sort of cradle of modern botany and herbaria”.
Since the 1970s, there has been a project to map the region’s entire flora, resulting in a database with more than 500,000 records.
Overall, the discovery highlights the importance of records of dried flowers, the researchers said. “A recent scientific trend is to dismiss these collections, which are regarded as dusty, cumbersome, unnecessary burdens – very expensive to stock and maintain and practically of no use for modern research. There is nothing more wrong: herbaria are indispensable and irreplaceable databanks for many research fields,” said Buldrini.
Global collections contain 390 million specimens, according to the Index Herbariorum. Buldrini added: “Dismissing them would be like dismissing our historical archives, our monuments or our art collections.”