It, like me, you struggle to tell one umbel flower from another then you will be relieved to find one that is quite unmistakable; The good news is that whilst the bulk of the umbels (or carrot) family are white the wild parsnip (Pastinaca sativa) is yellow. The bad news is that there are a couple of other yellow carrot family members too. That, though, should not be a major issue and a cause for confusion.
Wild parsnip is a bit like a yellow hogweed with a dense cluster of flowers. Whilst the cluster is formed of flowers from several small stems spreading out they form a relatively consistent or .condensed' flower head. There is space between the clusters but not a lot when compared to the two possible other yellow species, fennel and pepper-saxifrage. In these two other species each stem is some what dispersed from its neighbour giving a very different look to the flower than that of wild parsnip. There are other difference too, of course, but unless you are really keen there is not need to look any further. Before someone points out that Alexanders is yellow I would say that it is more green than yellow whereas wild parsnip is a bright, strong yellow.
The wild parsnip flowers from June until September and is a popular plant with pollen feeding insects. It is best left alone though as if you touch it you can develop some rather nasty blisters on your hands.Wild Parsnip: good news bad news