Blackthorn (Prunus spinosa) is not very common in Calderdale.
There are a few hedges around with plenty of Blackthorn in but then we don’t have that many hedges.
There are also a few old Blackthorns here and there, presumably relics from very old hedges.
I don’t think it is a local species.
Blackthorn flowers much earlier than Hawthorn and it flowers before it comes into leaf so it really stands out.

If you see what looks like a Blackthorn in full flower right now then have a closer look.
Even rarer in this area is Cherry Plum (Prunus cerasifera).
Cherry Plum flowers a little earlier than Blackthorn and the flowers open at the same time as the leaves.
So when I spotted this tree in blossom at Cromwell Bottom last week, across the river,
I had to find my way to it and see which it was.

So, I hear you cry, how do you tell which is which?
Well the twigs of Cherry Plum are green, they are brown/black in Blackthorn.
Cherry Plum lacks the long pointed thorns of Blackthorn
And Cherry Plum has reflexed sepals.
See here how the sepals are folded back and so when you look at the flower face on you only see the white petals.

But when you look at the Blackthorn flower you can see the green of the sepals between each petal.

I have very few records for this so please look out for it now and if you see it let me know.