Today at a Memorial Day cookout I noticed our local pines are shedding pollen. You may be familiar with this phenomenon from the thick yellow coating that turns up this time of year on rain puddles, picnic tables, and, most notably, your freshly washed car. Whence this bounty? Have a look pines’ remarkable pollen-producing powers:
Believe it or not, each pine pollen grain is actually an entire plant — the male gametophyte. Plants employ a system called “alternation of generations“, to which I’ve alluded before. The idea is that a diploid generation, or one with two copies of every chromosome, alternates with a haploid generation, or one that possesses but one. In some ancestral (aka primitive, aka less-derived) plants, both gametophytes and sporophytes (the diploid generation; in the case of pines — the tree) get big and live as a separate plants that look nothing like each other. Ferns are a good example of this; the gametophytes are tiny green sheets of cells hiding under leaf litter that you would never recognize as ferns.
In pines, the male gametophytes are the pollen, which come from their own separate male cones. Thus each pollen grain is actually an entire plant, and each little haploid plant is only two cells big: a tube cell, which will make the germ tube that seeks out the female gametophyte in the pine cone, and the generative cell, which will make the sperm. If you have pine pollen allergies here is what one of these little yellow misery-making plants looks like up close. Yes, that’s right: like Mickey Mouse. The “ears” are technically called the wings, and they help the wind-blown pollen grains sail about to find a female cone — or faux finish your car.
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