Fat hen (it was formerly used as a food for hens) is the commonest of all the goosefoots, which is the general name for Chenopodium species. Like many of the genus, it is covered by a silver-grey coating of swollen hairs giving it what is called a 'mealy' appearance.
It is a common weed of cultivated land, waste tips and disturbed soil.
All names: Chenopodium album agg. L.; Chenopodium reticulatum Aellen