The reason you can't find information on perennial basils is that there is no such animal (so to speak). ALL basils are botanically classified as annuals, though in some climates and in ideal conditons, certain varieties may survive for more than one growing season. Basils are very easily grown from seed, and tip cuttings are usually quick and reliable to strike. I have successfully propagated many different kinds of basil from very large cuttings with some hardwood attached. They need plenty of light and lots of heat. i always put them straight into potting mix or soil, after dipping the cut ends in pure honey (you can use hormone rooting powder or gel if you prefer, but I find the honey gives better results).

Try sticking a few cuttings in water until they root. This usualy works.

The Australian seed savers manual does state both perennial and annual basils !!

I have a perrenial basil plant that about 3 weeks ago I took about 7 cuttings of and just stuck straight into the dirt in the garden next to it and they seem to be doing fine. Also Ive found that pinching out some of the leaves means it grows 2 leaves back where each of the leaves were. Its getting pretty large now :)

I really like Thai basil.. I think I have some seeds here somewhere.. I think Ill grow that next time.. I like the taste better than normal basil or perrenial..

I propogate all my basils (Sweet, Thai, Lemon, Spicy Globe/minimum) mainly from cuttings, that way I get a plant just like the original as I grow all my basils together they look great especially the thai it's very pretty as well as good in asian dishes. Biggest problem growing them together is that the seeds are sometimes not true. I have sweet basil plants which have lasted for 2 years by cutting the seed heads before they are fully developed. The plant goes very woody and you have to be very careful not to prune too harshly. I pruned some too much and left only old wood and they died. When trimming make sure there is some new growth on the bush. They grow mad in my garden and self seed if I let them.

As above, easy from either seed or cutting. The only thing I do is nip out the growth bud and maybe some of the very soft tip growth. I find this improves the strike rate. Daisyduckworth's suggestion of dipping in honey is a good one as honey contains antibacterial and antifungal agents that help clean up the cut end.
There appear to be two plants both given the common name Perennial Basil - Ocimum americanum and Ocimum gratissimum, though they could be synonyms of course. I have what I think is Ocimum gratissimum and it has been happily growing for almost 3 years now. I don't think much of it as a culinary herb though. There are other much better tasting basils around.

I agree with Raymondo on this. I have an Ocimum gratissimum which I've had for a couple of years. It goes from strength to strength while the other (annual) basils come and go. I love it as a speciment and it smells initially pleasant if you just brush the plant, but crushing or chopping the leaves releases a rank camphorous / catnip odour which I don't find appetising at all.

Below is a website giving details of basil varieties. The basils which perform as perennials which I have growing are East Indian Basil (O. gratissimum) and West African Basil (O. viride or gratissimum).

Here is a link that might be useful: Basil varieties

I am happy to say that my basil usually survives quite happily for 2 years and readily self seeds.

The eden seeds catalogue details nine different basil varieties, the only one listed as a perrenial is O. grattissimum or the east indian clove basil. It says it grows to 1.5 metres and can be used as a clove sustitute, good in curries they say.

mudlark