I am an amateur attempting to discover the identity of everything that lives in my garden.
Photo's 1 and 2 (click to enlarge) show a weed that grows beneath the hedge at the rear of my garden (specifically, at (0.8,2.0) - see here). Turning to my copy of The Wild Flower Key (Francis Rose, publ. Penguin Books) I'm confident my weed is Herb Robert (Geranium robertianum).
Herb Robert is part of the Crane's Bill Geraniums, so-called as apparently the seed cases have that shape. I don't have a photo of this but will try to post one later in the season when the seed cases are well developed.
Left undisturbed Herb Robert has no particular smell, but bruise the leaves and a pungent odour emerges that, to my nose at least, is a cross between ginger and cat pee! Despite this off-putting feature, it seems some are happy to use Herb Robert as a herbal 'tonic' and it gets a mention in the famous writings of the 17th century English herbalist Nicholas Culpeper:
"Herb robert is commended....to stay-the-blood; it speedily heals all green wounds, and is effectual in old ulcers in the privy part"
Not advice I can endorse!
An obvious and intriguing question is who was Robert? Here, I have to say my web searches have drawn blank. According to this site possible candidates are a French monk Robert of Molesme (d.1110); Robert Duke of Normandy (d.1134) or a Bavarian St. Rupert of Salzberg (d.718). Whether these are the only candidates and which has the honour of being the one, true 'Bob I haven't been able to determine. If you're reading this and know, please leave a comment.
Richard Tofts has put a scholarly review of Herb Robert's biology online, from which I learn that the British Isles can be divided up into about 3,500 10x10km squares, and that you'll find Herb Robert in just about all of them. This prodigious ability to spread and colonise has led to G. robertianum becoming a serious problem-weed in woodland in the USA, where it is an introduced species.
For a fascinating photo of a Herb Flower taken in ultra-violet light (a region of the spectrum into which which many insects can see) see here. If you'll permit me a moment of hubris however, I have to say one of the prettiest photo's of Herb Robert I've seen is the one that emerged when I put a flower under my microscope at 40x magnification (photo 3) and saw the dozens of tiny yellow pollen balls clustering the flower's reddish-purple anthers (the presence of red or orange anthers identifies my plant as G. robertianum incidentally, rather than the similar-looking, though somewhat smaller, Little Robin (G. purpureum) which has yellow anthers).
Though to many gardeners it is a weed I shall leave my Herb Robert growing under my hedge. You never know when the ability to prepare a poultice that smells like cat pee is going to come in handy!