Asex'ual Spore (in plants). A spore which has not been formed by the union of two cells, that is, in a sexual way. Ordinarily, the asexual spore is formed by cell division. Its power of reproduction is the same as that of the sexually formed spore, the difference between the two being simply one of origin. Asexual spores are common among all groups of plants. They are the spores most commonly seen in connection with the flowerless plants, and among the flowering plants the so-called pollen grains are asexual spores. See Spore.