Palaeofloristic record of Linnaea borealis during the Mid-Holocene in the Friuli Venezia Giulia plain

Glacial relicts represent invaluable biogeographical markers of past climatic oscillations, offering unique insights into the historical dynamics of species distribution and the long-term persistence of biodiversity within refugia. Linnaea borealis , common name Twinflower, is a small suffruticose plant that grows in coniferous and mixed forests at altitudes ranging from 1,200 to 2,100 m a.s.l. This species is considered a relict of the Ice Age, as its current distribution is limited to circumboreal zones of the Northern Hemisphere. In Italy, currently it was observed living only in the mountains in four northern alpine regions (Valle d’Aosta, Piemonte, Lombardia, Trentino–Alto Adige), while fossil pollen records were found in a wetland area in the plain in Friuli Venezia Giulia. The finding in plains (30 m a.s.l.) in strata dated 6,000 years ago, i.e. significantly later than the post-glacial retreat, opens up the question of whether its disappearance did not occur in post-glacial times in the Palù basin, which possibly may have functioned as a refuge area for this species in the lowlands. This study focuses on the first evidence of past presence of this species, previously unrecorded and currently not present, in the Palù basin. Thanks to detailed palynological analyses, pollen grains of L. borealis were identified in Mid-Holocene pollen samples taken from a core drilled in this area. This approach underscores the importance of combining floristic and palynological data to reconstruct the biogeography and ecology of species. In the case of L. borealis , such analyses offer new perspectives on the past presence of this species in areas where it is no longer found today, shedding light on how climate changes during the Holocene may have influenced its distribution.