The enigma of the thornless thistle found in Sicily
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It is a thistle but has no thorns, exceeds three meters in height and disperses entire banks of seeds into the soil to regenerate after fires. Despite this the Greuter thistle it is a very rare plant and a loser, so to speak, because in nature it only grows in two canyons of Mount Inici in the province of Trapani. After the discovery of the first population in the late 1980s, another one has recently sprung up two kilometers away.
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This strange relative of the artichoke which has several similar species scattered in the Mediterranean does not have the right physique to tolerate the long Sicilian summer. The extra-large size of the leaves allows it to survive only in the shade of the cliffs where it can limit water losses to a minimum. To trace the exact distribution of the thistle in these inaccessible environments, the researchers of the CNR of Palermo also resorted to images captured by a drone capable of flying over the gullies without risking their necks.
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Greuter’s thistle, whose scientific name is Ptilostemon greuterihas long been a botanical puzzle. It is an authentic climatic relic that may have evolved on the north-western promontory of the Trapani area during the emergence phase of Sicily, when the island was only an archipelago.
“The woodiness of this thistle, its most enigmatic feature, is a property shared with other woody species that descend from herbaceous species that grow exclusively on oceanic islands such as Hawaiithe Galapagosthe Canaries or on the peaks of the equatorial mountains,” he explains Salvatore Pasta, researcher at the Institute of Biosciences and BioResources (IBBR) of the CNR in Palermo and first author of the recent study on thistle. From the base of these primordial atolls, when Sicily became a complete island, the thistle had to take refuge in the shady limestone valleys in order to survive. Beyond the confines of this cool, humid microhabitat, the plant’s days would be numbered. In the gorges and ravines of Mount Inici those mists are also condensed by the sea winds which ensure water to the thistle even in the most critical periods of the year.
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But the thistle has not only weaknesses. After all, it is a prehistoric species that has come down to us and it must have some tricks up its sleeve. “Despite being vulnerable to the climate, the Greuter thistle has remarkable fire-response capabilities arson that have regularly affected this area of Sicily for decades – adds the CNR researcher – in 2018 the main population of this plant was zeroed but the reaction was surprising. The specimens had already accumulated a large amount of seeds in the surrounding soil which allowed the species to recover when the flames died down.” It is as if the plant had prepared a plan B to prevent the effects of the fire.
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The two populations of thistle fall within a site of the European Natura 2000 network and according to the IUCN, the International Union for Conservation of Nature, this endemic species of the largest Mediterranean island is critically endangered. Yet it does not enjoy any specific form of protection.
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For safety it was grown in the botanical gardens of the universities of Palermo and Catania in Sicily and in that of Friborg in Switzerland. Even if the thousands of individuals discovered today appear to be in good health, a close chain of fires in the future could put an end to the species which has numerous young individuals, not yet able to create that supply of seeds indispensable to overcome the wave of fire .
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Now an international group of researchers between Italy and Switzerland is studying the most effective strategies to ensure the survival of Greuter’s thistle. Among the most promising solutions, an IT model is being tested which allows for the identification of both any hitherto unknown populations and the most suitable areas in which to introduce new plants in an attempt to improve the survival prospects of this Italian rarity.
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