Pollen Season

Ponderosa pollen_BlkForest-CO_LAH_7558-001For the past few weeks, my blue car has been yellow. Drifts of fine mustard-yellow dust cover our patio, our deck, and the floors indoors. I dust, and dust, and dust again; each time the rag comes up yellow. What is this dull yellow layer that covers everything? It’s pollen. More specifically, Ponderosa Pine pollen.

ponderosapollen - npsFor those of us who live with pine trees, the pollen season is a yearly event as predictable as the throngs of Miller Moths currently beating themselves to death against our windows, and happening at the same time of year. Because we had a lot of rain at the end of last summer, 2014 is particularly pollen-y. All those trees, once dying from thirst, have a new lease on life, and they’re taking full advantage.

Pine pollen used to confuse me. After all, we never notice flowers on the pine trees, so where does it come from? And why is there so darn much of the stuff? Both those questions have a single answer.

Leucanthemum x superbum_Shasta Daisies _XG_LAH_7067All flowering plants can be divided into two groups, angiosperms and gymnosperms. Angiosperms have their seeds enclosed in an ovary (fruit), and include most broad-leafed plants—daisies, roses, cherry trees, and the like. Their flowers are familiar, usually with petals and often containing nectar to attract pollinators. Even grasses, which lack such enticements because they’re wind-pollinated, are angiosperms.

Fir Cones_CheyenneMtnZoo-CO_LAH_6042-001Conifers, such as pines, firs, redwoods, and junipers, are gymnosperms. (So are Ginkgos, cyads, and Gnetales.) “Gymnosperm” means “naked seeds” and indeed, their seeds are not enclosed in any type of fruiting body. Gymnosperms have flowers too, but they look a bit different. We call these flowers “cones.” Usually, we just lump the various conifers together and say they all have pine cones, but that really isn’t correct. Firs have fir cones, piñon pines have piñon cones, and so forth. This photo shows a sap-covered female cone from a douglasfir tree.

Ponderosa pine cones_BlkForest-CO_LAH_7524-001Each conifer has both male and female cones. The female cones are the large, showy ones we pick up for decorations and crafts. Tucked between the scales of the developing cone are ovules that will, if pollinated, become seeds. The male cones, shown here and below, are smaller. They produce the pollen that’s driving us crazy.

Since the male cones and female cones are separate, pollen must somehow get from one to the other. Bees and other pollinators don’t visit conifers, so it’s all up to the wind. This is why there’s so much pollen—it increases the chances that some will get to where it’s needed. Looking outside, I’d say the odds are pretty good!

Ponderosa pine cones_BlkForest-CO_LAH_7529-001We could get more complicated. I could explain how the pollen on the male cone and the ovule in the developing female cone are both created through meiosis, resulting in haploid germ cells. Remember your biology? This just means that male and female cones each contribute one set of chromosomes to the new plant. (This is also true in people.)

When a grain of pollen reaches the ovule, it “sprouts,” growing a pollen tube leading to the ovule. Then the male DNA moves through the pollen tube to pair up with the female DNA inside the ovule. This is called fertilization. The resulting embryo is diploid, having two full sets of chromosomes. (People are diploid too.)

As the female cone matures, the embryo in each seed is protected with a seed coat, and food reserves are added to provide energy until the sprout can start making its own food through photosynthesis. Then it waits in a kind of suspended animation until the time is ripe to restart growth. Sometimes, all it takes is warmth and moisture. But many conifer cones stay tightly shut until a fire opens the scales, releasing the seeds to restore the burned forest.
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Pollen photo: National Park Service.
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