Automatic marijuana are those cannabis strains that will flower automatically and they don't require the light cycle change to start flowering. These strains have been made from the wild ruderalis strain that has low THC levels but high CBD and they are also more pest resistant and they can grow in colder climates and harsher conditions. These wild ruderalis species were cross-pollinated with regular cannabis strains high in THC and the autoflowering children that were the most potent were selectively chosen to again cross pollinate and stabilize the autoflower trait and high THC levels. Basically the modern autoflowering strains are regular weed plants with the added benefit of the autoflower gene that lets them flower by time not by light cycle
first autoflowering strains appeared on the market around the turn of the 21 century and have been growing in popularity ever since!