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... while trying (and failing) to find a way of explaining why it's Alliaria petiolata, rather than Tussilago farfara.
The best I can offer is that the latter has more angular leaves.
If you look at this posting http://www.ispot.org.uk/node/343606 and look at the leaf edges you can see the differences in shape.
Chris Brooks - www.dragonfly-images.co.uk
My Flickr site - www.flickr.com/photos/ceb1298
... Alliaria petiola (love the way that rolls off the tongue) often has wiry black stems under those umbrella-like leaves, whereas Tussilago tend to be shorter, and green.
That's my non-botanical contribution.
Oh, and if you bruise (crumple) the leaves, this one smells seriously unpleasant, ie garlicky.
How to take close-ups with cheap phone and hand-lens:
Field Guides for Budding Botanists:
Lat/Lng: 52.6, -1.2
OS grid ref: SK5604