research of Olympus's plants started in 1836, when the French botanist Aucher-Éloy studied them. According to this and later studies, the National Park of Olympus is considered one of the richest flora regions in Greece, with about 1,700 species and subspecies, that represent some 25% of Greek flora. Of them 187 are characterized as significant, 56 are Greek endemic and of them 23 are local endemic, i.e. they can be found only in Olympus, and 16 are rare in Greece or/and have there the limits of their spread within Northern Greece. An important book about the plants and flowers, from the beach of the Aegean Sea up to the upper regions of Mount Olympus, was written in 1980 by the Swedish botanist Arne Strid. Most of those found in lower elevation are the common Mediterranean and central European species. Ramonda heldreichii (syn. Jankaea heldreichii), a plant relict of the Ice age, is of particular interest to botanists. The intense diversity of the landscape, the varying orientation of the slopes and their position in relation to the sea affect locally Olympus's climate and so a local microclimate prevails, combined with the geological background and the soil favor the growth of particular vegetation types and biotopes. Generally Olympus's northeast side is densely forested, as it receives the most rainfall, while the southwest one has significantly sparser vegetation. Flora zones In Olympus there are generally four sequential flora zones, but due to the complex topography and variety of microclimates, these do not form an obvious clear sequence with elevation. Mediterranean vegetation zone A zone of evergreen broadleaf trees (maquis) occurs between 300 and 500 metres elevation. Along with oak (Quercus ilex) and Greek strawberry tree there occur kermes oak, strawberry tree, Phillyrea latifolia, bay laurel, cedar and others. Of the deciduous species most common are Fraxinus, Ulmus, Montpellier maple, Judas tree, terebinth, Cotinus coggygria and others. Forest zone of beech, fir and mountain coniferous The evergreen broadleaf trees' zone is gradually replaced by ecosystems of European black pine, that forms compact clusters, with no intermediate zone of deciduous oaks, although trees of these species occur sporadically within clusters of black pine. On the northern slopes of Xirolakos valley, between 600 and 700 metres elevation, there is a high forest of downy oak of about 120 hectares. The black pine dominates on the eastern and northern side of the mountain, between 500 and 1,700