Oceanic climate with thermal averages corresponding, for example, to those of Portugal and uniformly distributed rainfall postulates the presence of Rhododendrum ponticum in the breach of Hottinga, of a local form of this together with Acer laetum Aesculus hippocastanum and to other elements of the so-called Pontic flora in insubric phyllite deposits that are usually referred to the Ryss-Wurmian interglacial, while that of Re in Val Vigezzo (Ossola Valley) where the rhododendron was also found more recent and, therefore, postglacial , that of Calprino, etc. The penetration of the Atlantic component that the Negri has traced in the Piedmontese and Tuscan flora and which has its most typical exponents in the clayey and fresh soils and in rainy sectors must have occurred in successive waves coinciding with oceanic phases that also pushed the beech to vegetate at a lower altitude than the current one or in isolated districts such as the Euganei, the Gargano, etc. On the other hand, Laurus canariensis , la Persea amplifolia and indica , Ilex canariensis , Zelkova crenata and acuminata (the first three Canarian types, the last two Asian) recognized by Béguinot in phyllites from the surroundings of Palermo referable to a recent Quaternary and perhaps to the Ryss-Wurmian interglacial. Their disappearance must be ascribed, rather than a new hardening of the climate, to its increasing drying up and this factor must have made its influence felt, for example, in the group of the Maltese islands, a remnant of an Afro-Sicilian cavity already rich in vegetation as evidenced by the vertebrate fauna and the very presence of the papyrus, a resurgence plant, which disappeared only in the first half of the last century, and the poverty of paleoendemisms despite a relatively ancient emergence of this land.
According to timedictionary, the climatic fluctuations that occurred after the last glacial peak – the Wurmian – and which were documented, among other things, with the analysis of the fossil pollen found in peat bogs and marsh gangos have been widely studied outside Italy. The few data collected so far by us do not allow generalizations: we will only say that the Achen oscillations tend to refer to that kite (Kerner) or xerothermic (Briquet) period, during which Mediterranean species and some of the same components of the scrub and wood evergreen have been able to radiate and expand, forming, in the foothills of the Alps and especially in the more propitious slopes of the lake basins and sometimes penetrating into the same valleys, those thermophilic colonies that we have mentioned in its place. Quercus ilex , Cistus salvifolius with its parasite Cytinus , C. laurifolius (disappeared at the beginning of the last century), Erica arborea , Arbutus unedo , Spartium junceum , Ruscus aculeatus , Asparagus acutifolius , with around the thermal-mineral springs at the foot of the eastern slope Polypogon monspeliensis , Lepturus incurvatus , juncus acutus and maritilleni Dillenius , Speri , Aster tripolium , Sonchus maritimus, and other halophytes that have disappeared today, testifying an ancient beach line and overall a more pronounced thermophilicity than at the current coast. Noteworthy is the presence of isolated colonies of Ruta patavina , whose closest stations are in Poreč and Postumia and which is an oriental element irradiated from Asia Minor in Greece and then, through Illyria, up to Istria and then in the Paduan, and the Mediterranean scrub that covers some islands of Quarnaro, southern Istria and some points of the Gulf of Trieste is of trans-Adriatic irradiation. Conversely, the Cistus laurifolius (already existed in the Euganean), the C. albidus between Torri del Benaco and Albisano (Garda), the Aphyllanthes monspeliensis at Dragoncello near Brescia they evidently radiated from western territories. A salient feature of these colonies is their isolation and this suggests that immigration was favored by a warmer and drier climate than the present, which is the supposed xerothermic, but in the Euganean some type may be prequaternary. The steppe colonies, for example, of the Val Venosta, mentioned above, have a different origin and constitution, but it is not yet clear which climatic phase they should be synchronized with.
Finally, it should be noted that the anthropic factor exerted an action in Italy, the cradle of ancient civilizations and the scene of the most diverse immigrations, particularly profound and which still continues and even intensifies. It is to this that we owe the destruction of a large part of the early forests, the drying up of vast swampy areas, the protection of some species at the expense of others for which the natural ecological relationships were disturbed, the settlement of Prato formations where c ‘it was wood, or artificial meadows, the creation of some new conditions such as ruins and fertilizers that recalled associations of nitrophilic plants (nettle, parietary, chenopods, etc.), but more than anything else, the introduction of many exotic plants or a rational exploitation of the indigenous ones in that cultural landscape that masks the same natural one in some sectors. A very complex action, therefore, which was carried out especially in the submontane area; and it is enough to think of the wide glimpses of its forest mantle, the introduction of the chestnut tree or its exploitation where it existed, the extensive development of viticulture and olive growing which, moreover, has in common with the coastal districts. But enough has been said about the main crops in the alps and apennines. With the seeds of cultivated plants, man has unknowingly introduced numerous species, some of which remained confined to crops and others passed to pollute natural formations. The release of ship ballast, the introduction of wool, rice-growing in Padania, artificial meadows, were as many points of settlement of exotic species from which some radiated and spread. But another starting point was the same intentional cultivation of foreign species that have found in our soil exceptionally favorable conditions to propagate there, such as the Robinia pseudoacacia along the railway embankments and in the landslides, the American Agave and some Opuntia (prickly pear) planted in the south and in the islands at the edges of the fields and along the roads, which have become an integral part of the botanical landscape and here are remembered the Tulipa , the Narcissus , the Coronary Anemone cultivated and perfected by selection and hybridization in the ancient gardens of some cities (Florence, Bologna, Lucca) and then escaped from cultivation and naturalized to such an extent as to lie in the appearance of plants that have arisen in the state of nature. Overall, Béguinot and Mazza have enumerated 538 exotic species found in the adventitious state, of which 216 recognized naturalized and some that have become pests such as Oxalis cernua in the fields and citrus groves of southern and insular Italy, Galinsoga parviflora and Acalypha virginica in the vegetable gardens of north and central, the Azolla caroliniana and filiculoides and the Helodea canadensis in calm waters, some Cuscuta parasitic in artificial lawns, Oenothera biennis in marine arenas and alluvial sands, etc.