From the Questions
page (check it out - it has cool pictures, too):
Since sarsaparilla (botanical Aralia nudicaulis, Spanish sarza - bramble or shrub, parilla - vine, also called Smilax), also called sassparilla (sassafras & sarsaparilla) and sas'parilla, is almost always flavored primarily with sassafras, and the additional spice of sarsaparilla (and very few people can taste any difference between sarsaparilla and root beer made by the same company), Root Beer World considers sarsaparilla to be root beer. For a different view, see Sarsaparilla vs. Root Beer.
“So here’s a tribute toast with root beer in hand to you and the many mugs of suds along your happy trails.” --Charles Wysocki, artist and root beer fan, 1928-2002