From Wikapedia
Cannabis ruderalis is a species of Cannabis originating in central Russia. It flowers earlier than indica or sativa, does not grow as tall, and can withstand much harsher climates than either of them. Cannabis ruderalis will produce flowers based on its age, rather than light cycle (photoperiod) changes which govern flowering in sativa and indica varieties. This kind of flowering is also known as "autoflowering".
The term ruderalis is derived from the Latin rūdera, which is the plural form of rūdus, a Latin word meaning rubble, lump, or rough piece of bronze. A ruderal species refers to any plant that is the first to colonise land after a disturbance removing competition
Cannabis sativa, indica, and ruderalis are all species of the genus Cannabis. They can all inter-breed freely, and many 'pedigree' cultivars are indica/sativa hybrids. Authorities disagree about the number of species of plant which constitute the genus Cannabis. Although many authorities continue to class all varieties of the plant, including hemp and marijuana, as Cannabis sativa, it is widely accepted that there are three separate species or sub-species. sativa, the most widely cultivated in the Western World, was originally grown on an industrial scale for fiber, oil, and animal feedstuffs. It is characterised by tall growth with few, widely spaced, branches. indica, originating in south Asia, is also known historically as Indian hemp, and is characterised by shorter bushy plants giving a much greater yield per unit height. ruderalis is a hardier variety grown in the northern Himalayas and southern states of the former Soviet Union, characterised by a more sparse, "weedy" growth. It is rarely cultivated for its THC content.
Similar ruderalis populations can be found in most of the areas where hemp cultivation was once prevalent. The most notable region in North America is the midwestern United States, though populations occur sporadically throughout the United States and Canada. Large wild ruderalis populations are also found in central and eastern Europe, most of them in Lithuania, Belarus, Latvia, Estonia and adjacent countries. Without human selection, these plants have lost many of the traits they were originally selected for, and have acclimated to their environment.
Cannabis ruderalis has a lower THC content than either sativa or indica, so it is rarely grown for recreational use and the shorter stature of ruderalis limits its application for hemp production.[citation needed] Cannabis ruderalis strains are high in the cannabіnoid cannabidiol, so they are grown by some medical marijuana users.
However, ruderalis' early, plant-age triggered "autoflowering" characteristic (which offers some agricultural advantages over the day-length flowering varieties) as well as its reputed resistance to insect and disease pressures makes it attractive to plant breeders.[citation needed] indica strains are frequently cross-bred with ruderalis to produce autoflowering plants with high THC content, improved hardiness and reduced height