Some my find this title surprising. Alder trees have flowers?
To a botanist, a flower is anything that produces seeds and fruit (in the case of plants like alders with separate male and female flowers, the pollen-producing flowers also count, of course). There is no requirement that they be showy.
Yes, alder trees bear fruit as well as flowers! To a botanist, a fruit is anything that surrounds a seed. It doesn’t have to be fleshy, juicy, or edible. The tiny, dry wings that surround alder seeds are as much a fruit an apple or an orange.
The photograph above shows clusters of both male (large, dangling catkins) and female (the smaller, erect catkins at top) flowers. Those male catkins released clouds of yellow pollen when I gently brushed them.
The alder pictured above was not taken on Bainbridge Island and is not the Red Alder (Alnus rubra) so common on the Island. It is a Sitka Alder (Alnus viridis ssp. sinuata). I took that photo in the Olympic Mountains.
The Sitka Alder is much smaller than the Red Alder, typically being only a large shrub or small tree, making it far easier to find flowers in easy shooting range. Sitka Alders have glossier leaves, which are sharper-toothed than the Red Alder’s. The Sitka Alder’s leaves are not curled under slightly at their edges like the Red Alder’s are. The Sitka Alder is mostly a mountain tree, while the Red Alder is a common lowland species. One of the favored habitats of the Sitka Alder is avalanche slides; for this reason it is sometimes called the Slide Alder.
If all that leaves you a little confused, fear not! That particular Sitka Alder happened to be growing in the altitude range where the two species overlap, right next to a Red Alder sapling. I snapped a picture showing the two side by side (Sitka on the left, Red on the right).