Pollen isn't something comes to mind when most people think about traditional foods, but there's a number of culinary traditions around the world that use it to make specific dishes.
Commonly used varieties
So far I've only cooked with pine, cattail, and fennel pollen. Cattail and pine pollen are generally used in sweets and baked goods in place of a proportion of the flour.
I usually harvest from the males cones of Red Pine, and is harvested in the spring when the cones are filled to bursting. The harvest window is extremely short-only a day or two. \
To Harvest Pollen
Using a large zip-top bag, bend a branch on the tree so the cones filled with pollen go into the bag. Rub the cones around with your fingers to release the pollen into the bag.
Sift the pollen when you get home and store it in the freezer as it will go rancid at room temperature.
Cattail pollen is harvested in the early summer. I think it has the most robust yeasty flavor of any I've tried, but, as is it's much easier to harvest from pine trees in volume for most people I don't work with it much.
Fennel pollen is usually sprinkled on top of dishes to finish them. It has a mild anise flavor and is more comparable to an herb than pine or cattail pollen.