Cowslips are a common sight in April and May – brightening up grasslands and motorway verges with their swathes of nodding yellow flower heads. When I first started out in botany, I spent a good while convincing myself that the cowslips were indeed cowslips and not oxlips – Rose’s wildflower key tells you that cowslip is like oxlip but the ‘leaves are more wrinkled and the stem is more gradually tapered to the base’ which requires a certain amount of experience to compare! Luckily the sniff test (cowslip flowers smell like apricots) saw me right!
One simple rule of thumb is location – true oxlips are a rare ancient woodland species restricted to the part of the country where the counties of Cambridgeshire, Suffolk and Essex meet. Unless you are in a location like this, you are unlikely to be encountering oxlip. But to be on the safe side, here’s a few more pointers!
Cowslip – Primula veris
The flowers of cowslip, like those of oxlip, form a nodding head facing in a single direction. They can be long-stemmed – up to 25cm tall, but are often shorter where the nutrient levels are lower. The flowers are deep yellow with orange flecks in the centre.
You can find up to 30 flowers in a flower head, or sometimes just a few. Remember to take a sniff – the apricot aroma is quite distinctive in a fresh flower!
Oxlip – Primula elatior
Oxlip, as mentioned above, is a rare native found in ancient woodland in a restricted area of the country. If you are encountering the species on a roadside verge or in a meadow in Nottinghamshire, it’s probably not an oxlip. However the species can be bought as a plant, or grown from seed, so it is quite possible it can spring up in unexpected places if it escaped the confines of its sowing!
The oxlip is similar in structure and stature to the cowslip, in growing to ~25cm high and having 10-30 flowers on a head. As with the cowslip, all of the flowers will be nodding on the same side of the stem.
The oxlip flower is less bell-shaped than the cowslip, with more open spreading petals and a lighter, paler yellow. The centres of the flowers lack the orange spots usually found with cowslip.
False oxlip – Primula vulgaris x veris
Just to add to the confusion, there is another species which can be confused with both cowslip and oxlip and this is the false oxlip. The latin name is Primula vulgaris x veris reflecting the fact that a false oxlip is in fact a cross between a primrose and a cowslip, occuring where these two species are found in close proximity. If you find something which you suspect to be an oxlip outside of the correct habitat and geographical area, a false oxlip is your most likely suspect!
The flowers are more open and spreading, a little like an oxlip, but you can see the telltale orange flecks which indicate the cowslip parantage. Rather than nodding in a single direction, as a pure oxlip or cowslip would do, these flowers face in all directions. There is significant variability in the character or these hybrids, with some being closer to the primrose parent and some more strongly representing cowslip.
Grantham Ecology 
By accident I have arrived at your blog. Upon looking through the pages my attention was drawn to the picture of what you call Oxlip. Are you sure it is Oxlip? Your excellent photo convinces me that the plant is a Cowslip. These are the characters that I have used to identify the plant.
[1] The flower in your picture is more bell shaped than I would expect for an Oxlip. The Oxlip flower is much more open, [more like that of a Primrose].
[2] The Cowslip flower is a much deeper, brighter yellow than the Oxlip which is usually a pale yellow.
[3] The calyx of the Cowslip is uniformly pale green but that of the Oxlip has darker, green midribs.
If the hairs on the plant in your photograph were clearly visible that would also help determine the species. The hairs of the Cowslip are short and straight while those of the Oxlip are short and crisped.
[Reference: ‘New Flora of the British Isles’ by Clive Stace]
From a member of the BSBI.
You’re entirely right; how embarrassing to have mixed it up in the photo for an ID post, sloppy captioning! Thanks for your additional ID comments too – although I was concentrating on that one characteristic, the others from Stace make for a much more robust guide to differentiating. I’ll try to add an oxlip photo next spring for comparison.
Thanks again for taking the time to correct my mix-up!
Here’s my posting on Westfield Wildlife from a couple of years ago about these two species and a hybrid, in case it’s of interest! http://westfieldwildlife.wordpress.com/2012/04/20/primrose-cowslip-and-a-hybrid/
Actually my posting was about Cowslip and Primrose, and their hybrid ‘false Oxlip’, as well as Oxlip 😉
fascinating – thanks for sharing! 🙂 are they still thriving in the garden?
Does the Oxlip have no scent at all or just not that of apricots?
I thought an easy way to tell them apart is that the flowers of cowslips hang down (like udders!) but oxslips are more horizontal
This year, what seemed to be primroses have mad in my garden. I still don’t know without doing the sniff test whether they are cowslip or oxslip but at least I now have a better idea of what is going on!