Getting plant sex wrong (3)

Continuing my tendency to be irritated by descriptions of botany in the popular literature, I’m now reading The Forest Unseen: A Year’s Watch in Nature. I’m not too impressed with the book in general, but here’s a bit that’s particularly irritating (end of the chapter “March 25th – Spring Ephemerals”):

This intricate web of dependency dates back one hundred and twenty-five million years to when the first flowers evolved. The oldest fossil flower, called Archaefructus, had no petals, but its pollen-bearing anthers had flags on their tips. The botanists who described the fossil believe that these extensions may have been used to attract pollinators. Other ancient flowers also appear to have been insect-pollinated, further supporting the idea that insects and flowers have been partners since the first flowers evolved. How this marriage came about is unknown, but it seems likely that flowering plants evolved from fernlike plants. These ancestors produced spores that attracted insects looking for an easy meal. The ancestors of the flowers turned the plague of insect predators into a blessing by producing conspicuous displays to attract these spore munchers, then producing so many spores that thee insects’ bodies would be coated. The predators inadvertently carried some of this sporey dust onto the next flower, increasing the fecundity of the spore producer. Eventually the spores got wrapped in a package, the pollen grain, and the true flower was born. The bees and spring beauties in the mandala reenact the main theme of the original relationship. The bees, or their larvae, eat most of the pollen they gather, transferring only a small number of pollen grains from flower to flower.

To say “it seems likely that flowering plants evolved from fernlike plants” is somewhat misleading and at least unhelpful. Flowering plants are not particularly closely related to ferns; various of the ancestors of flowering plants back around their common ancestor with the gymnosperms might have looked vaguely ferny, but not in any way that is relevant to the evolution of pollination. But that’s not really too big a deal, it’s just a minor annoyance. The big irritation is here: “Eventually the spores got wrapped in a package, the pollen grain, and the true flower was born.” First – a pollen grain is not a package of spores. Each pollen grain begins as a single spore. Then one or more (the details depending somewhat on which lineage we are talking about) cell divisions take place inside the spore wall, and you have a group of cells inside the original spore wall, which persists more or less unchanged. If we’re doing academic botany, we call that an endosporic microgametophyte; in popular writing there are any number of less technical ways to say “several cells inside a spore” but “a package of spores” is just wrong. Second – pollen predates flowering plants, so identifying the origin of pollen with the origin of flowers is also wrong. All the gymnosperms, which do not produce flowers, do produce pollen. A few of them (Ephedra, for instance) even produce structures that look an awful lot like the stamens of flowering plants. The defining morphological feature of flowers, as compared to the cones of gymnosperms, is the carpel.