A new light method to identify the hawthorn

Behind their spines and small white or pink flowers, the hawthorn hides a real scientific headache. With nearly 300 species in North America, these however common shrubs remain very difficult to identify, even for specialists.

Étienne Léveillé-Bourret, professor of biology and curator of the herbarium Marie-Victorin, and his doctoral student Marc-Aurèle Vallée have developed an innovative method which could well change the situation and contribute to a better identification of these unknown species.

But, what is a species?

Identifying a hawthorn is not just about observing its leaves or thorns. Their biology complicates the task: “Some hawthorn has three or four copies of each chromosome and can also reproduce without sexuality, producing seeds which are clones of the mother plant”, explains the professor. This particularity facilitates the production of hundreds or thousands of individuals with the same genetic differences … without necessarily forming real distinct species.

“Botanists from the time of Marie-Victorin tended to name each small variation as a different species. Today, we have to unravel all of this, ”says Marc-Aurèle Vallée. He himself defines a kind of hawthorn as “a distinct evolutionary line that can be differentiated morphologically and genetically”. He still recognizes that the border remains vague: “There is still debate on what a species is really.”

A “light barcode” to differentiate them

Faced with these difficulties, Étienne Léveillé-Bourret and his student had an original idea: using light to identify the hawthorn. “We analyze how the leaves reflect light in the visible and infrared spectrum. It gives a kind of luminous barcode, different from one species to another, ”illustrates Marc-Aurèle Vallée.

This technique, spectrometry, can even apply to old specimens. “Over time, color and other visible characteristics disappear in the herbaries. But spectrometry still reveals chemical and structural information in dried leaves, ”he adds.

Initially, this technology was used to map the vegetation of tropical forests from drones. But his performances convinced the team to adapt it to the hawthorn. “It worked so well that I use this approach almost more often than the laboratory of Etienne Laliberté, who had bought the device at the origin”, jokes Étienne Léveillé-Bourret.

Faster and cheaper than genetics

This approach also has a major asset: cost. “A spectrometry apparatus costs tens of thousands of dollars, but once acquired, the only expense is the time for the analysis. More than thirty specimens can be treated per day, ”says Marc-Aurèle Vallée. Conversely, a genetic analysis can cost $ 30 or more per sample and require several weeks of delay before receipt of the results.

Above all, the “spectral barcode” sometimes seems more efficient than the “genetic barcode”, which works better in animals. “With the genetic barcode, we know that it is a hawthorn, but not always which one. Spectral barcode seems to be better allowed to distinguish them, ”observes Étienne Léveillé-Bourret.

A promising method for other species

This method could help solve other taxonomic puzzles. “The hawthorn was an ideal group for testing this technique, because they have leaves wide enough for taking measurements. But that could apply to many other difficults that are difficult to distinguish, ”says Marc-Aurèle Vallée.

For the researcher, beyond the classification, one of the challenges is conservation. “It does not matter that we call these entities of species or genotypes, they are part of the diversity that we want to protect. And this can then have an impact on ecosystems, by hosting insects or [agents] different pathogens. And even directly on our health, given that the hawthorn is very studied for their medical potential. ”