Indica has chemicals that are antagonists to THC and help counteract it; Indica gives the "body buzz: or "Couch lock" feeling. CBD also helps with pain. Sativa has very little CBD and gives the "Dude, have you ever looked at your hands" type high.
Hemp and marijuana are the same thing; the difference is which traits are emphasized. Ruderalis is a small plant with little production; it is also auto-flowering (Doesn't need a change in light cycle to flower)
If you haven't guessed, I have my card.
Here's WIkipedia's version:
A total of 46 varieties of hemp with low levels of tetrahydrocannabinol (THC) are certified by the European Union (EU). They have, unlike other types, a very high fiber content of 30-40%. In contrast to cannabis for medical use, varieties grown for fiber and seed have less than 0.2% THC and they are unsuitable for producing hashish and marijuana. The most important cannabinoid in industrial hemp is cannabidiol (CBD) with a proportion of 1 to 5%.
Image: black and white drawing: C. sativa tall, C. indica middle, C. ruderalis small [The variety of appearances for cannabis. Only C. sativa (left) is suited for industrial hemp, but it also has medicinal varieties.]
The variety of appearances for cannabis. Only C. sativa (left) is suited for industrial hemp, but it also has medicinal varieties.
Cannabis sativa L. subsp. sativa var. sativa is the variety grown for industrial use, while C. sativa subsp. indica generally has poor fiber quality and is primarily used for recreational and medicinal purposes. The major difference between the two types of plants is the appearance and the amount of 9-tetrahydrocannabinol (THC) secreted in a resinous mixture by epidermal hairs called glandular trichomes, although they can also be distinguished genetically. Oilseed and fiber varieties of Cannabis approved for industrial hemp production produce only minute amounts of this psychoactive drug, not enough for any physical or psychological effects. Typically, hemp contains below 0.3% THC, while cultivars of Cannabis grown for recreational use can contain anywhere from 2% to over 20%.