Leeks are a good example of the second botanical term used in that knotweed quote; polyploidy. One of the techniques used by nature to aid evolution is to develop extra sets of chromosomes. This gives a species greater adaptability. In effect, a greater range of traits to allow it to fit varying habitats and circumstances. It also turns out to be very useful to horticulture. Chrysanthemums, in all their fantastical varieties, are a good example of horticultural manipulation involving polyploidy. Horticulturalists can now even induce a plant to produce more sets of chromosomes by introducing chemicals that have that effect. Centuries of unnatural selection have created the modern leek, which is now usually considered a separate species from its ancestor, Allium ampeloprasum. Leeks have been reported wild from AR, IA, IL, KS, NY, OH, and TX. Cultivated, my garden, 7/3/14. Onion family, Alliaceae.