When I was growing up, my parents grew mint in the garden. This was used occasionally for making mint sauce for lamb and such like. Then down in the sweet shop there were Polo mints and XXX mints etc, and these tasted very different to what we refered to as 'mint' in the garden. There were also 'spearmint' varites of Polo mints and other sweet mint varietes. Later in life I discovered mint tea, but one mans mint was another mans spearmint or peppermint it seemed. So some investigation was in order.
Peppermint (mentha x piperita) , probably the most widely available mint in "mint tea", is actually a hybrid of spearmint (Mentha Spicata) and watermint (Mentha Aquatica).
Spearmint seems to be what was growing in my garden all those years ago, the spear in the name coming from its pointy leaves. However spearmint seems to have some wide range of flavours depending on its cultivation. The mint I like these days and most closely recalls the mint from the family garden is called Moroccan Mint. From what I can gather it is actually a cultivation of spearmint called 'Nana'.
Minty taste comes from an oil called R-carvone, present to a greater or lesser degree in different varieties and cultivation of mints.
There are currently recognised 25 pure species of mint and 6 hybrids (of which peppermint is one).
There you go... Wasn't that interesting? :)