fasciation

An abnormal form of growth in which a shoot becomes enlarged and flattened, giving the appearance of several shoots fused together. It is often seen in dandelions (Taraxacum). It may be caused by mechanical injury, by fungi or mite attack, or by infection with a bacterium of the genus Phytomonas, especially P. fasciens. In some plants, e.g. cock's comb (Celosia argentea cristata), it is due to a mutation.