Rare species in past pollen records and herbarium specimens: Linnaea borealis L. lived in north-eastern lowlands in Italy during the Neolithic

This paper emphasises the role of detailed pollen identification in past records and the importance of historical herbaria in palaeoecological research on plant distribution over the last millennia. Palynological analyses of a sediment core, covering approximately the last 10,000 years, from the wetland surrounding the UNESCO archaeological site of Palù di Livenza, in the lowlands of Friuli-Venezia Giulia, revealed the unexpected presence of Linnaea borealis during the Mid-Holocene (about 8600–4200 cal yr BP) in north-eastern Italy. This species is a rare small suffruticose plant which grows among mosses in conifer and mixed forests, between 1200 and 2100 m a.s.l. In Italy, due to the restricted climatic requirements, its current distribution is limited to a few high-mountain stands and to four northern regions (Val d'Aosta, Piedmont, Trentino-Alto Adige, Lombardy). Pollen grains of L. borealis found in past samples from the Friuli-Venezia Giulia region raised interest because this species was not recorded so far in this region either at present or in the past. To confirm the identification, a morphological study was carried out on pollen from flowers collected from University Herbaria (Florence and Pisa). Dried pollen extracted from anthers was acetolysed and observed with a Digital Optical Microscope. Polar axis, equatorial axis, exine thickness, equatorial diameters, mesocolpium, and distance among apices of colpi were measured in current and past pollen grains. Morphological analysis confirms the presence of L. borealis in the sedimentary archive studied, adding an important insight into the knowledge of past and present biodiversity of the area. • Detailed palynological analyses provided high-resolution insights into local flora biodiversity. • The study of past pollen samples stimulated new morphological research. • Use of herbarium specimens for an in-depth analysis of pollen grains of target species.