Ginseng
Species
Panax chinensis: includes Chinese ginseng and Korean ginseng
Panax quinquefolius: American Ginseng
"Siberian ginseng" is not ginseng. It is Eleuthuro senticossus, and is not very closely related at all. It has some shared properties but is a different herb entirely and looks quite different.
Varieties: sometimes ginseng will be described as red or white. White ginseng was cleaned, steamed, and dried after collection. Red ginseng is treated the same way, but other herbs (often considered to be fiery in nature) are added during the steaming process which darkens the color of the root to a ruddy brown. Generally red ginseng is considered to be warmer and more strongly energizing. White ginseng is better in Yin deficiency patterns where excessive heat could aggravate things. Either species can be prepared "red" or "white".
Grading: roots are generally graded by age and size / thickness. Ginseng is very expensive for two main reasons. #1, wild ginseng is very rare and will generally command higher prices than a farm raised root of the same age and similar weight. #2, cultivated ginseng takes a long time to grow. Ginseng roots need to be a minimum of 6 years old to be viable as an herb for human consumption. Prices increase dramatically as age goes up (100+ year old wild roots sell for hundreds of thousands of dollars at auction) but even for a farm raised crop harvested at 6 years of age the investment of time required to bring a crop to market is outstanding. It's not like an orchard that takes 6 years to be viable and then spits out fruit. It's 6 years of waiting and then you dig up the roots and that's it, one harvest and start again. And you can't even use that field again right away, it has to go fallow. Ginseng is notorious for sucking nutrients out of the soil.
Classical properties: Chinese ginseng is considered to be a lung and spleen qi tonic (an important note here, the traditional Chinese medicine concept of the spleen is more akin to a meta organ that includes the physical spleen and the pancreas and is ultimately considered to rule over all digestion much like the pancreas does).
Essentially this means that it's really good for strengthening respiratory, digestive, and overall metabolic function. It's excellent for immune health (which is intimately related to the lungs and GI tract which are the major sites of immune activity because the outside world is contacting the inside of the body in these two systems), it is a premium herb for endurance and stamina (coming off of the respiratory and metabolic benefits), and it also has a host of other beneficial properties which tend to fall within those patterns.
Now American ginseng is considered to be very similar to Chinese ginseng in strength and properties with the difference being that it is more Yin (and thus it is more appropriate for patients who become overheated or agitated easily, it is more strongly moistening, etc) and more cooling in nature.
Korean ginseng is exactly the same as Chinese ginseng with the exception that selective breeding and different methods of preparation with "red" ginseng yield a final product that is more warming and more fiery in nature. Korean ginseng would be cautioned in persons who get overheated easily. It would be one of the worst herbs to give to a woman who experiences hot flashes for example.
