Documents dating back to the 16th century reveal the origin of one of Charles Darwin's landmark studies may have been stretched back centuries before the famed scientist was born.

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 dubbed them "heterostyly," the University of East Anglia reported. Darwin published this hypothesis in the Natural Selection in the Origin of Species only a year before observing the phenomenon in nature himself. These findings led Darwin to uncover the origin and consequences of this reproductive system.

New research suggests Darwin was not the first to observe heterostyly, and they had been published in several 17th and 18th Century botanical records, and even some dating back to the 16th century.

 "Darwin is widely [recognized] 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," said lead researcher Prof Phil Gilmartin, from UEA's School of Biological Sciences. "But while looking through illustrations from the book Flora Londinensis by William Curtis, I 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."

The researchers noted they already knew heterostyly had been described as far back as 1583, but this study is the first to trace the history of the idea through three centuries.

"Science had clearly moved on by the time of Darwin -- but we have traced the origins of his work right back to what we think are the very first observations of heterostyly, some three centuries before his landmark paper. At least seven botanists, through the ages either drew or described the two forms of flower before Darwin made his observations. But they just didn't make the connection and [realize] the significance of what they were documenting," Gilmartin said.

Representations of the phenomenon were seen in Wilibald Artus' Hand-Atlas sämmtlicher medicinisch-pharmaceutischer Gerwärchse (1848) and in William Curtis' Flora Londinensis (published on March 1, 1791), who used the words "pin-eyed" and "thrum-eyed" almost 100 years before Darwin. Darwin's own grandfather Erasmus Darwin had corresponded directly with William Curtis in November 1781 to comment on the Flora Londinensis.

"It is surprising that Darwin wasn't aware of Curtis' work. But from the evidence we have gathered, it is clear that he did not know about the engravings and descriptions of pin and thrum flowers in Flora Londinensis," Gilmartin said. "His mentor Henslow was however aware of the images. But despite illustrating the two forms of flower himself, he did not publish them. Had he done so he would no doubt have cited Curtis' prior observations."

Three images dating back to 1614, 1611 and 1605 are believed to be the first to show the differences between Primula pin and thrum flowers, earlier than that they were not pictured together.  A Latin text from 1583 by the botanist Carolus Clusius is believed to be the first description of long and short style forms of Primula flowers.

"By the time Darwin published his follow-up Different Forms of Flowers in 1877, he had discovered that heterostyly had been previously observed and documented," Gilmartin said. "The early botanists simply did not [realize] the significance of what they were documenting. Back in 1583, Clusius was focused on detailed observation -- but as highlighted by [Dutch botanist and scholar] van Dijk he did not [recognize] that both forms are found in the same species. Had he done so, he could have provided us with the earliest description of the two forms of flower 279 years before Darwin."

The researchers pointed out a "difference in attention to detail" prevented earlier scholars from noticing the significance of these floral morphologies or the reason behind these differences.

"That is what Darwin [realized], where others had only observed. Indeed, in his 1887 autobiography, Darwin wrote that 'no little discovery of mine ever gave me so much pleasure as making out the meaning of heterostyled flowers'," Gilmartin concluded.

The findings were published in a recent edition of the journal New Phytologist.