|Rough Hawkbit, Leontodon hispidus. High Elms Country Park, 2 June 2013.|
Some of them dominate a particular field or area. At High Elms, there are Rough Hawkbits. They are generally very hairy, and have sepals that clasp the inflorescence.
|Cat's-ear, Hypochaeris radicata. Spring Park, 5 June 2013.|
|Beaked Hawk's-beard, Crepis vesicaria. By Hayes Station car park, 12 June 2013.|
So once you know what to look for, you can tell most of them apart quite easily. Of course, this is far from the full set, and you sometimes need to see the leaves as well. Also, some of them flower at different times of year. The true Dandelions have been going for a while, but these three are just at their peak now.