common plant in my garden
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If you could provide a photo of a well-developed basal leaf, a clearer shot of the stem leaves and an idea of the width of the flower an ident is quite likely.
It looks as though the basal leaves are probably cordate, which, given that the stem leaves are not petiolate (as we can see from the photos), narrows the search down to C. officinalis and C. pyrenaica. Probably C. officinalis but more info needed.
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Here in Leicester we have a large amount of a Scurvygrass growing at the sides of major roads, presumably due to salinity from winter gritting operations.
... Cochlearia danica now grows along the edges of minor roads as well. I've even seen it the best part of a thousand feet up. (That particular road also has Spergularia marina, and, I think, Puccinellia distans.)
Lat/Lng: 50.8084, -0.0591
OS grid ref: TQ368027