Wintercress Barbaria vulgaris and allies
Wintercress is around for much of the year, but it is the basal rosette of winter leaves that are best for the kitchen. It is a weed of cultivation and seems to like ploughed, disturbed and muddy environments. A favourite habitat is on the mud dug up by helpful councils when clearing ditches. It is common throughout most of lowland Britain. Nevertheless (and for some obscure reason) I seldom come across it. This the reason for it not making into the book, not its flavour, which is very good.
It is in the cabbage family and has a certain amount of pepperiness. There is another species, an import called American Wintercress, Barbarea verna. It is very likely that the specimen pictured here is that species, but it is almost identical and there is no difference at all on the plate.