Calamus commonly refers a group of plants, usually Sweet Flag or Acorus calamus. It is an amazing herbal medicine, and can be used to cure toothaches.
American vs. European
There are two forms of common calamus, or sweet flag: American and European. The two have not been distinguished until recently. Both grow wild in the United States, but the American variety is native to the country. Sometimes the american variety is refered to as Acornus Americanus, instead of Acornus Calamus, however most vendors do not differentiate between the two. The american variety is considerably less toxic.
Japanese Sweet Flag
Japanese Sweetflag, or Acorus gramineus is rarer form of sweet flag. Rumour has it that it can be smoked, an uncommon method of ingestion for sweet flag.
Potency and Effects
In large doses calamus can be very potent, while in small doses it is simply relaxing. Most people do not enjoy the taste and only get mild effects. It can be chewed and used as an very effective method of toothache relief.
Fresh calamus is considerably better than old calamus, so when buying or picking make sure you ingest it fairly relatively quickly. It may not stay good for longer than a year or two (estimate, needs citation).