I was walking along the track through the high boggy area (clue!) when I noticed that an earth wall - created to deter joy-riders - had become covered in little rosettes of young plants. I always like to test my identification skills on vegetative states, so I began to mentally catalogue the species I found.
I thought you might like to do the same.
First, an easy one. Leaves about 12mm long:
Another easy one. Leaves about 6mm long:
I think this is less easy, but there is a strong clue in the picture. Leaves about 10mm long.
This one is definitely more difficult. The leaves are about 5mm long, and show a feature that will (according to some references) readily identify the species, although this feature is difficult to find later in the season, when you would like it to be there to resolve disputes.
This could be a stumbling block unless you think laterally. Leaves about 12-15 mm long:
Last clue: two of the species are very closely related.