I will take the opportunity of this botany picture to illustrate how a professional botanist identifies an unknown species. Imagine me walking along, finding this growing as an ornamental hedge, and taking a little branchlet home to identify. The next steps were as follows:
1. Cursory examination of the flowers reveals 4-merous flowers with strap-like petals. Taking this together with it being a woody plant, my gut says Hamamelis, but they generally have yellow flowers and bloom before the leaves unfold. As the picture above shows, our unidentified species blooms with leaves present and is quite clearly purple-flowered. Better not get fooled, try an identification key.
2. Think that this would be a good moment to put to use the fifth volume of the Rothmaler flora of Central Europe. It covers cultivated plants, and there seems to be a good chance that this ornamental shrub would be in there. Closer examination of the book shows, however, that it only covers herbaceous species. Darn.
3. My wife suggests Fitschen's Gehölzflora, a flora covering all woody plants growing in Central Europe. I consult the index and home in on the identification key titled Gruppe V: Blätter einfach, wechselständig, ganzrandig (group V: leaves simple, alternate, with entire margin).
4. I get nowhere but frustrated. I realise that the key uses only leaf characters. Surely there will be alternatives? Further consultation of the index reveals the so far overlooked Schlüssel zum Bestimmen der Familien vorwiegend nach Blütenmerkmalen (key for the identification of plant families using mostly flower traits). Great!
5. The key leads me to the Hamamelidaceae. Perhaps my gut feeling wasn't so bad then. Sadly, however, it then leads me to the genus Hamamelis where I find that all the listed species have yellow flowers and bloom before the leaves unfold, as mentioned above.
6. Bugger that. I cannot be the only one who sees this plant and thinks it might be Hamamelis. Let's google "Hamamelis purple" and see what comes up. Ah, that one looks like it. Loropetalum chinense, comes in a white variant and in the purple variant rubrum. Popular ornamental shrub. Hamamelidaceae, but not a genus I had ever heard of before. Okay then.
We like to think that the usual procedure is either "botanist recognises plant, done" or "botanist consults identification key, keys out species, done". Reality is rather less straightforward. Having a broad knowledge of plant families helps, however; I should have trusted my instincts from the start.