You can find numerous buddleja cultivars in garden centres. The Royal Horticultural Society site has a picture of seventeen of them. As far as I'm aware mine is not an artificial cultivar (can anyone confirm this from the photo?).
The buddleja in my garden grows vigorously and I regularly need to prune it back. True to its common name, it is a magnet for butterflies and other insects - an example being the peacock butterflies I photographed recently feeding there.
Amongst the many pleasant consequences of my self imposed mission to blog my garden is the discovery of so many excellent web resources. In preparing for this posting for example, I came across the excellent UK Biological Records Centre, a database of 15million entries on 12,000 UK species. Amongst the resources, the centre offers a downloadable database providing information on all the alien species of plant and animal to have invaded the British Isles. From the database I learn that Buddleja davidii was first grown in the UK at the famous the Kew Gardens in 1896, and it was not until 1922 that the first wild 'escapee' was recorded (at Harlech in Wales - how seed travelled the several hundred miles from Kew to Harlech I can only imagine!). The latter date surprised me - if I'd been asked to guess, I think I'd have imagined buddleja to have been imported by some intrepid seventeenth century plant hunter. These days you'll see Buddleja davidii on almost any patch of rough, stony ground in the UK and I've been told that it was extremely common on bomb-sites at the end of the second world war; To have spread so widely since only the 1920's is a testament to its hardiness (mine has survived having being ripped out of the ground by the bulldozers of the builders who did some work on my house a few years ago for example!).
The species name daviddii refers to one Father Armand David, a French Catholic missionary and keen naturalist. The first Westerner to discover it, Father David found Buddleja davidii growing on gravel river beds in China in 1876 (or 1869, depending on which web site I look at - does anyone know which is correct?). Father Armand had a prodigious talent for discovering plants and animals: over a thousand new species (including the giant panda - none of those in my garden as far as I'm aware!).
The genus name Buddleja is a reference to the Reverend Adam Buddle (1662-1715) an Essex botanist whose collection of moss, grasses, seaweeds and lichens is today housed in London's Natural History Museum. Mark Lawley's site includes a biographical essay. The name Buddleja was coined by Linneaus in honour of the Rev. B - the Reverend himself never actually encountered the plant. 'Buddleja' is Linneaus's spelling, although it's common to see the alternative 'Buddleia'.
And finally, a little microscopy? But of course! For no more reason than its intrinsic fascination value, some buddleja pollen (photo 3, 400x magnification, click to enlarge).