The significance of spines in Cardueae is tested through the analysis of their position in the different organs and their variations in different Moroccan stations. It appeared that the most constant presence of thorns is linked to capitule bracts. We also show that the spines are mostly developed in areas with arid stage and mild to hot winter, and areas with semi-arid to sub humid stages with fresh winter. The climatic conditions prevailing in these areas allow a moderate biomass productivity. It is hypothesized that the development of spines is an adaptation to prevent damages to mammal grazing, and especially to protect capitules, where inulin reserves accumulate in the receptacle.