Dandelion-type flowers can be a real trial for even the experienced botanist on occasions so what chance have we amateurs got? Well, with a little thought, we have a chance with some and this one, nipplewort (Lapsana communis), is a good start.
Nipplewort is a fairly tall plant growing to a metre or more tall and so it cannot be a dandelion. The plant has multiple flowers on shorter branches emanating from a central stem so it cannot be a dandelion. The leaves are not toothed they are fragmented and they do not form a basal rosette but grow out from the central stem so it cannot be a dandelion. The flowers themselves are quite small and simple whereas a dandelion has bold, complex flowers. Nipplewort is a common plant of shady hedgerows and woodland whereas dandelions are found in the open in grassy areas. Hopefully you are getting the idea!
Nipplewort is part of a 'subset' of the dandelion family known as hawkbits and, with experience and using the various features of the flower it is possible to distinguish between them but it does take practice.
So, you are all asking "Why is it called nipplewort?". Simply because the unopened flower bud is said to resemble a nipple!