In many natural and semi-natural habitats trees and shrubs represent two major growth forms (1). In
particular shrublands, which can be considered a mixture of several sclerophyllous shrubs and tree species,
represent a Mediterranean type of vegetation rarely found in other ecosystems. The distribution of shrubs in
an ecosystem is connected to complex ecological processes. Indeed, shrubs provide substrate, food and
shelter for organisms, play an important role in the nutrient cycle providing organic matter input to soils and
they protect watersheds from erosion. Moreover shrubs are very important for many associated species such
as mammals, birds, invertebrates, other plants (that favour thanks to their role of nurse plants), and their
distribution also influences the variety and abundance of mycorrhizal fungi, fundamentals in ecological
terms and nutritional relationships (2). This study represents a review on the ecological role of some selected
Mediterranean shrubby species. In particular the attention is focused on the following species: Amelanchier
ovalis Medik, Astragalus nebrodensis (Guss.) Strobl., Crataegus laciniata Ucria, Lycium intricatum Boiss.,
Prunus spinosa L., and Viburnum tinus L. These species have been selected because they are representative
of different Mediterranean vegetation types, distributed in relation to the bioclimate type and the altitude. In
fact, various habitats have been considered in relation to these species, for example coastal and sub-coastal
environments for Lycium intricatum, sclerophyllous woodlands for Viburnum tinus, mantle vegetation and
pre-forest structures for Amelanchier ovalis, Prunus spinosa and Crataegus laciniata, orophilous thornycushions vegetation for the Sicilian endemic Astragalus nebrodensis. For each species the geographical distribution in the Mediterranean Basin has been investigated, considering its borders according to the limits of Mediterranean climate (3), and the definition of terrestrial ecoregions of the world (4). The species
distribution as well as their taxonomy (especially in relation to the presence of subspecies in the Italian
territory) have been analyzed thanks to a number of scientific publications and web-based sources (e.g. Euro + Med PlantBase, The International Plant Names Index, ILDIS- International Legume Database & Information Service, PAN-European Species directories Infrastructure, Portale della Flora d\u2019Italia, Flora of Greece Web, Anthos, African Plant Database, Silene-Flore database, etc.) at regional, national and
international scale. Moreover for each species distribution maps have been prepared geo-referencing the species location data obtained from the labels of digital herbaria samples of the Mus\ue9um National d'Histoire Naturelle, MNHN \u2013 Paris, P; Naturhistorisches Museum Wien, W; Herbarium Mediterraneum Panormitanum, PAL; Herbarium Plant Biology Section, CAT; Botanischer Garten und Botanisches Museum
Berlin-Dahlem, Zentraleinrichtung der Freien Universit\ue4t Berlin, B, and from the data portal Global
Biodiversity Information Facility- GBIF (always in relation to herbarium samples), also in order to obtain
historical distribution data. The ecological role of species in every ecosystem, but also of their successional
dynamics and their response to global changes and disturbances was investigated making an analysis of the
literature data and also in relation to some botanical aspects and functional traits, available for some of the
studied species, from TRY Plant Trait Database (https://www.try-db.org) and form BROT 2.0 database, for
example: Growth form, Leaf phenology, Spinescence, Flower color, Dispersal mode, Fruit type, Nutritional
relationships (the analysis of these data is in progress especially with regard to mycorrhizal symbioses). This
has allowed to clarify why shrubs are successful in many habitats and to evaluate the critical role that they
play in Mediterranean ecosystems