Alder tree catkins put on great display
ALDER TREE catkins put on a great display during February and March. Alders belong to the birch family, a small family of plants with just seven members, all trees and shrubs: Silver Birch, Downy Birch, our native and common Alder together with two alien alders widely planted for shelter and timber, our native Hazel and finally Hornbeam, an alien tree occasionally found in demesne woodlands.
Since Alders grow best in damp places they are usually to be found on riverbanks, on lake shores and in damp woodlands. Farmers often plant a grove of them in a wet corner of a field where few other plants are likely to thrive.
Alders reproduce by means of catkins rather than by means of what would generally be regarded as 'regular' flowers. Both sexes are present in the one tree and both have catkins. While there are male and female catkins they are so totally different that they cannot be confused with each other.
Male catkins are crimson and yellow, are long, slender and dangling and hang downwards from the tree's branches. Female catkins are red, short, stubby and are located above the male catkins.
The male catkins produce pollen. Being long and dangling the catkins shake and toss about in the breeze. Ripe pollen grains are cast adrift in very large numbers into the ocean of air and the breeze bears them along in the completely random expectation that one of them will get stuck on one of the sticky female flowers in the small female catkins on another tree.
It seems amazing that such an apparently haphazard way of reproducing works but it does. Key factors that have led to evolutionary success are that the males produce very large amounts of fine, dust-like pollen and they do so in spring before the leaves come on the trees.
As the male catkins die off, the bracts of fertilised female catkins swell and the female catkin grows into an olive-shaped, green, woody fruit. The weight of the seed-bearing fruit causes it to hang downwards.
When the seeds are ripe the fruit opens and sheds them. Old fruits persist after the seeds have been shed and may be seen on Alder trees at present resembling small, open pine cones together with the fading remains of the long, dandling male catkins.