Living on a development of bungalows build back in the 1960's our roads do not get much attention from the local council. That is not a complaint, I am actually quite pleased as we get all manner of wild flowers growing in the gutters and along the pavements and walls! I had never seen thale cress (Arabidopsis thaliana) until we moved here back in 2006 but it is quite common around our local roads.
Although quite a common weed of cultivation it does not generally occur on lime soils and much of the cultivated fields of Dorset and Hampshire are on the chalk downs. I am sure that is one of the reasons I missed it previously but there is another reason I suspect. Thale cress is a small, frail plant with just a few tiny four-petalled flowers at the top of the stem, easily overlooked in a field but less so in a roadside gutter.
The amazing thing about thale cress is that despite its very small flowers they create long, thin, cylindrical seed pods which point upwards. This distinguishes it at once from the similar shepherd's purse whose fruits are very different.
Thale cress is now used extensively in botanical research because of its very simple genetic structure.