Least Yellow-sorrel

As Ben only has one lecture on a Wednesday, I opted to have a walk round Stamford in the summer sun while I was waiting for him.Despite having visited so frequently last year, I still managed to add about fourteen plant species to the tetrad total, including this Least Yellow-sorrel, which was growing in a stone wall and along some pavement cracks. 

I only saw this small yellow annual, which hails from Australia and New Zealand, for the first time about four years ago, but I now find it quite frequently, especially in churchyards. It seems to be increasing in the midlands, possibly in response to milder winters.