Numerous segetal weeds have their origin in the flora of the Near East (SW-Asia). Between about 9000 and 7500 BC arable farming originated in SW-Asia. From the Middle East, one of the gene centers on earth, agriculture spread along three routes into SW-, NW- and NE-Europe. About 4400 BC on loess soil in the southern part of The Netherlands Triticum monococcum, Triticum dicoccum and several weeds are found in neolithic bandkeramic settlements. In Roman times several species of mediterranean origin immigrated into The Netherlands. The cultivation of root-crops on large scale is much younger. Life forms, spectra of dissimination, periodicity and the distribution of archeophytes and neophytes differ from vegetations under winter-cereals and root-crops (including summer-cereals) and of ruderal sites. Species with a limited atlantic area, e.g. Galeopsis segetum, are of special interest. Differences between weed vegetations under winter-cereals (Secalietea) and root-crops (Polygono-Chenopodietalia) are not determined by the cultivated crops but by agricultural measures (season of tillage of the land) and by soil conditions (fertility and moisture). Temperature determines the germipation of winter or summer annuals. The associations of Secalietea and Polygono-Chenopodietalia can take each others place from year to year, but the associations of Secalietea are best developed when many years after each other winter-cereals are cultivated.