Now surely no one can mistake this for a dandelion? I know it is yellow and has lots of florets in the flower head but it bears no other resemblance to a dandelion at all. This is the commonest of the hawk's-beards, smooth hawk's-beard (Crepis capillaris).
The flower of the hawk's-beard is much, much smaller than a dandelion and the main stem keeps branching with a flower appearing at the top of every stem whereas the dandelion has a single central stem to support one flower. The outside florets on the edge of the each flower head is tinged with orange as the flower opens. Many of the lower flowers will have turned to seed before the top ones have even opened so each plant has a long flowering period and, again, the seed head is very different from a dandelion, it is much more contained within the sepals and does not open out into the glorious globe of a dandelion clock.
I said this was the commonest of the hawk's-beards in Dorset the only other one likely to found out of the seven listed in my reference book is the similar beaked hawk's-beard. However, they are easy to tell apart if you look at the developing flowers as the buds are pointed (giving the appearance of a beak) whereas the smooth has round flower buds.
In flower from June through until the frosts kill it off in November time you can find it along roadsides, on waste ground, and grassy places in general including lots of it on my lawn; and there you have it, a crude beginners guide to hawk's-beards!Smooth Hawksbeard: a weed of neglected lawns