The Blackthorn (Prunus spinosa) also has a mass of white blossom. Now the first buds open, well before the leaves.
The flowers of the Blackthorn are smaller as those of the Plum. They sit an nearly black branches. In autumn this bush produces small blue fruits.
Generally it is a bush of less than 1.50 m high. The Blackthorn is invasive, new branches develop from the spreading roots, and it can overrun a large surface. End of March edges of woods, hedges ant left-over pieces of land can be covered in white blossom like snow. The Blackthorn has - not surprising - big black thorns, and where they grow in dense stands they are literally inpenetrable.