The probability that a species becomes alien outside its native distribution range is determined by the size of its native range and tolerance to a wide range of climates acquired in the region of origin. Biological traits play only an indirect role at this stage of invasion via determining the size of the native range.Species ability to become weed is determined not only by the above characteristics of native distribution, but also directly by biological traits (life form, strategy, early flowering, tall stature, generative reproduction, number of ploidy levels and opportunistic dispersal by a number of vectors).