Milk thistle (Silybum marianum) is a ruderal, nitrophilous plant, native to the Mediterranean basin with natural adjacentdesert populations. It is usually utilized for its hepatoprotective activity due to its high content of silymarin; a complex of seven flavonolignans: silybin A, silybin B, isosilybin A, isosilybin B, silychristin, isosilychristin, silydianin, and one flavonoid, taxifolin. In Israel, it grows in almost all regions, from the upper Galilee in the north to the edge of the Negev desert in the south, including the Jordan Valley and around the Dead Sea. The aim of the current study was to analyze S. marianum populations from three Mediterranean regions; in northern, central and southern Israel, adjacent to the Negev desert, for silymarin content and composition, in order to evaluate their potential significance as sources for medicinal purposes. Seeds collected from all regions were planted in a screen-house under Mediterranean conditions in central Israel. The resulting F1 progeny was planted in an open field and their seeds were evaluated for silymarin content and composition. Silymarin concentration and content per plant highly varied among all populations, ranging from 21 to 36 (gr/Kg) and 3.3 to 12.3 (gr), respectively. In general, the highest silymarin concentration was measured for plants originated from central populations and the highest silymarin content per plant was measured for the central and northern populations. Analysis of silymarin composition revealed unique chemotypes in all regions, and particularly in central Israel, combining significantly elevated levels of the most potent compounds according to Polyak et al. (2010; PNAS 107:5995-5999) of taxifolin, isosilybin A, silybin A, silybin B and a mixture of silybin A and silybin B. We concluded that the high variation in climatic conditions across Israel contributed to the appearance of unique chemotypes, having great potential for future varieties cultivated for silymarin. Recent Publications 1. Degani A V Dudai, N Bechar A and Vaknin Y (2016) Shade effects on leaf production and essential oil content and composition of the novel herb Eucalyptus citriodora hook. Journal of Essential Oil Bearing Plants 19(2): 410–420. 2. Cohen-Zinder, H Leibovitz, Y Vaknin, G Sagi, A Shabtay, et al. (2015) Effect of feeding Moringa oleifera Lam. silage to lactating cows on digestibility and efficiency of milk production. Animal Feed Science and Technology 211:75–83. 3. Vaknin Y Dudai, N Murkhovsky, L Gelfandbein, L Fischer R and Degani A (2009) Effects of pot size on leaf production and essential oil content and composition of Eucalyptus citriodora hook. (Lemon-scented gum). Journal of Herbs Spices and Medicinal Plants. 15:1–13. 4. Steinitz B, Tabib Y, Gaba V, Gefen T, Vaknin Y (2008) Vegetative micro-cloning sustaining biodiversity of threatened Moringa species. In Vitro Cell. Dev.Biol.-Plant 45:65–71. 5. Vaknin Y Hadas, R Schafferman, D Murkhovsky L and Bashan N (2007) The potential of milk thistle (Silybum marianum L.), an Israeli native, as a source of edible sprouts rich in antioxidants. International Journal of Food Sciences and Nutrition 20:1–8.