'Darwin correctly decoded sexual behaviour of Primroses'

New documents dating back to the 16th century have given a unique insight into one of renowned naturalist Charles Darwin's landmark study into the sexual behaviour of the Primroses.

According to molecular biologists from University of East Anglia in Norwich, Britain, at least seven botanists drew or described the exact sexual behaviour of the flowering plant before Darwin made his observations.

"But they just did not make the connection and realise the significance of what they were documenting and Darwin provided the exact scientific explanation," the team observed.

In 1862, Darwin presented the case that some plant species have two floral forms that differ in height and arrangement of the male and female sexual structures and named it "heterostyly".

These are either the "pin" form where the female organs are elongated and the male organs are shortened or the "thrum" type where the female parts are shortened and the male organs are extended.

"Darwin is widely recognised as the first to study pin and thrum flowers in Primula and importantly, he was the first to provide an explanation for the functional significance of the two types of flower," explained lead researcher professor Phil Gilmartin from the school of biological sciences.

Darwin published his hypotheses of "Natural Selection in the Origin of Species" (1859) - just a year before first noticing "heterostyly".

The breakthrough influenced him to eventually unravel the origin and consequences of this reproductive mechanism.

While looking through illustrations from the book "Flora Londinensis" by famous British botanist William Curtis, professor Gilmartin was struck by a Primula print which showed the two types of flower captured in a copper plate engraving dating back to the late 1700s.

"It predated Darwin's observations by more than 70 years," he noted.

Little did Darwin know that his own grandfather Erasmus Darwin had corresponded directly with Curtis in November 1781, expressing his delight with the "Flora Londinensis".

"It is surprising that Darwin was not aware of Curtis' work but it is clear that he did not know about the engravings and descriptions of pin and thrum flowers in 'Flora Londinensis'," the authors said.

This realisation triggered a journey into archives of botanical texts, letters, copper-plate prints, and drawings dating back to the 16th century - in search of earlier documents that could have influenced Darwin and the origins of his idea.

"We already knew that 'heterostyly' had been described as far back as 1583," Gilmartin noted in the new paper published in the journal New Phytologist.

The work pulls together all the existing documentation, including early floral prints, to trace the history of the idea - over three centuries.

Darwin's correspondence reveals that his breakthrough was assisted by his children, who gathered 522 flower stalks for his studies.

But his contemporary Freidrich Hildebrand was not so fortunate. He was thwarted when his plants were "destroyed by children in the botanical gardens" in Bonn, Germany.

Other botanists to notice the two forms of flower include Darwin's former Cambridge tutor and mentor John Stevens Henslow who had drawn both in 1826.

Records show that the two forms of flower were also documented in the 1818 volume "Flore Medicale" (Medical Flowers) by French botanist and physician Francois-Pierre Chaumerton.