Vegetation diversity along the altitudinal and environmental gradients in the main wadi beds in the mountainous region of South Sinai, Egypt

South Sinai includes Egypt’s highest mountains that resemble an ecological island surrounded by desert. The present study aims to analyse the vegetation physiognomy along the altitudinal and environmental gradients in the main wadi beds in South Sinai mountainous region. This includes determining the natural, native-weed and alien vegetation in representative stands in this region, analysing their vegetation in terms of species composition, abundance and life forms and determining the national and global distribution of the associated species. This investigation also aims to describe the prevailing plant communities and assess the role of environmental conditions that affect the vegetation in this region. Thus, thirty-two stands were chosen during March–June 2018 to reflect the prevailing altitude and environmental gradients. Total species was 316 (229 genera and 61 families): 186 species were perennials (58.9%), while 130 were annuals (41.1%). In addition, 152 species were native weeds (48.1% of total species), 31 were aliens (9.8%), along with 133 natural species (42.1%). Eight species were recorded as endemic to Egypt: Anarrhinum pubescens, Euphorbia sanctae-catharinae, Hypericum sinaicum, Origanum syriacum subsp. sinaicum, Phlomis aurea, Primula boveana, Rosa arabica and Solanum sinaicum. In addition, 10 species were recorded as near-endemics to Egypt and other adjacent countries: Allium desertorum, Asclepias sinaica, Centaurea scoparia, Fagonia mollis var. hispida, Hyoscyamus boveanus, Iphiona mucronata, Micromeria sinaica, Pterocephalus sanctus, Salvia deserti and Stachys aegyptiaca. In the present study, 33 species are threatened and categorized as follows: 8 endangered, 8 vulnerable and one indeterminate, while the rest were evaluated by the authors as rares. The rich plant diversity of this region is due to its extensive mountainous massif, which supports many microhabitats. The high elevations in this region hinder the dispersal process of propagules, a situation which often tends to increase endemic and near-endemic species. The current results were discussed and compared with some related previous studies.