Sloe (blackthorn) blossom is produced before any leaves appear, often in such profusion that whole hedgerows can look as though they're covered in snow.
Wild cherry (gean) blossom - clusters of large flowers set against expanding foliage that has a bronze tint when it's young.
Male ash flowers. Ash trees flower long before their leaves expand - this is usually the last tree species to come into leaf, in May. There are three basic kinds of ash tree. All-male trees like this produce dense clusters of crimson pollen-producing anthers when their flower buds burst. All-male trees never produce ash 'keys' in autumn.
Female trees produce clusters of flowers with bright red stigmas and styles - the style will later develop into the wing of the ash 'key'. Female trees produce heavy crops of 'keys' in autumn.
Close-up of female ash flowers. There are also hermaphrodite trees, whose flowers look similar to these female flowers but have a pair of pollen-producing anthers attached on either side of those slender green stalks. They too produce heavy crops of 'keys' in autumn.
Just to complicate matters even further, some trees produce any two of the above three flower types on the same tree i.e. male + female; male + hermaphrodite; female + hermaphrodite.
For more information on trees click here