Hoax, gibberish or perhaps even the work of aliens, the Voynich manuscript has been baffling scholars for years. But now a botanist says he has unravelled the mystery of the untranslatable document, claiming that the medieval text is written in a language from central Mexico.

Looking at the plants illustrated in the manuscript, Arthur Tucker of Delaware State University and his colleague Rexford Talbert were "immediately struck by the similarity" of the xiuhamolli/xiuhhamolli or "soap plant" shown in the 1552 Codex Cruz-Badianus, also known as the "Aztec Herbal", to a plant drawn in the Voynich manuscript.

"Both depictions have a large, broad, gray-to-whitish basal woody caudices with ridged bark and a portrayal of broken coarse roots that resemble toenails," write the scientists in a paper published in the journal of the American Botanical Council. "The portrayals of both of these Mesoamerican species are so similar that they could have been drawn by the same artist or school of artists."

The enigmatic manuscript, which is dated to the 15th or 16th century, is filled with botanical, figurative and scientific drawings accompanied with undecipherable text. Running to more than 200 pages, it was bought for 600 gold ducats by Emperor Rudolph II of Germany around the end of the 16th century, and then vanished until it was acquired in 1912 by the Polish-American antiquarian bookseller Wilfrid Voynich. It is now housed at Yale University.

Previous Voynich researchers have assumed the manuscript has a European origin, but after studying the plants, Tucker and Talbert suggest it might come from Mexico. Another plant in the manuscript previously identified as "viola tricolor of Eurasia", they say, is actually native to North America, and is the viola bicolor.

In total, they believe they have linked 37 of the 303 plants drawn in the Voynich manuscript, six animals and one mineral to the geographical region "from Texas, west to California, south to Nicaragua, pointing to a botanic garden in central Mexico".

They say the style of the drawings in the Voynich manuscript is also similar to 16th-century codices from Mexico, and state their belief that while "loan-words for the plant and animal names have been identified from Classical Nahuatl, Spanish, Taino, and Mixtec", the main text of the document "seems to be in an extinct dialect of Nahuatl from central Mexico, possibly Morelos or Puebla".

The botanists have met with some scepticism. Gordon Rugg of Keele University, whose research in 2004 pointed towards the Voynich manuscript being a hoax, told the New Scientist that the plants depicted in the manuscript could be nothing more than a forger's invention, adding "if I sat down with a random plant generator software and got it to generate 50 completely fictitious plants, I'm pretty sure I could find 20 real plants that happen to look like 20 of the made-up plants".

But Tucker believes the identification of the viola bicolor is crucial: he says the distinction between the viola bicolor and tricolor was only clarified in the 20th century, and meanwhile the Codex Cruz-Badianus was not discovered in the Vatican archives until after 1912. "If somebody created this as a hoax prior to 1912 then they had to have knowledge of botany … that was only published after 1912," he told the Guardian. "If it was a hoax, then we have to invoke Jules Verne and his time machine."

Tucker says his paper "was primarily written to propose a new paradigm, since over a hundred years of fiddling around has not deciphered one word that matches the plants, and the plants that have been identified by others suffered by the a priori assumption that this was European".

"Right now we are pursuing other lines of evidence that will be more definite and not subject to interpretation as identification is," he said. "However, there is still the main text to decipher, and until this is deciphered, we have not truly unlocked it."

In their paper, Tucker and Talbert acknowledge that "because we have been trained as botanists and horticulturists, not linguists, our feeble attempts at a syllabary/alphabet for the language in the Voynich manuscript must be interpreted merely as a key for future researchers, not a fait accompli. Much, much work remains to be done, and hypotheses will be advanced for years," they write.