Sex and the alder

The Alder Alnus glutinosa is monoecious, that is to say that it produces both male and female flowers on the same the same tree. The penduline male flowers or catkins are initially a dark red wine in colour but turning yellow as they open, by which time they are about 2 inches long.
 
The female flowers are much smaller in size, cone-shaped and red. When fertilised, they become green fruits, which gradually become woody and eventually release small, reddish brown seeds. The dry female cones often stay attached to the tree until the following spring, as in the bunch on the right of the photograph.