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.

The im­age above shows this year's prom­i­nent male catkins, small fe­male catkins above them in a group of three and last year's old, open and woody cones.

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