Ferns Are 400 Million Years Old

—Michael Penziner, FRNC Docent

Tree ferns in Golden Gate Park, San Francisco. Photo: Paul Downey on commons.wikimedia.org.

Well okay, not exactly our ferns here at the Rye Nature Center. We're talking about how long ago ferns developed in the world. They are among the first of the vascular plants. And by vascular, we mean that they have a means of transporting water up to the top and then down again, basically the way animals have veins and arteries. Because of how early ferns developed they're a bit different from most of the plants we're familiar with, so we thought we'd tell you a bit about them.

We probably all remember that plants have male parts (stamens) and female parts (pistils); that a pollinator or the wind gets the pollen from the stamens and deposits it on the pistil, and that pollination occurs that way. Fruit forms from that process, and seeds develop in the fruit. But that's not the way it happens with ferns. When ferns first developed, the world had not yet completely figured out plant sex, so there was no male and female. A fern did not reproduce with a seed because it was asexual; it reproduced with something called a spore, which of course was also asexual. The spore falls on the ground, develops roots, and grows into something called a prothallus. That prothallus somehow becomes a sexual body, with both male and female organs. Here's the surprise: the male organ in that prothallus is filled with sperm, exactly as in animal reproduction. When the female organ is ready, it emits a pheromone, signaling the sperm that it is fertile. The sperm in turn swim around the prothallus to the female side and fertilize it.

Well, some hundreds of years ago people, who were very well aware that plants reproduced with seeds, couldn't figure out where the fern seeds were, so they came to what they thought was a logical conclusion. If they couldn't find fern seeds, those seeds must be invisible. The way to get them, they thought, was to put twelve pewter plates under the fern, and recite a certain incantation at midnight on Midsummer's Eve. The seeds would then fall through the first eleven plates and land on the twelfth. Well, now that they've done that, what happens next? They thought that if you collected those invisible seeds and put them in your pocket, you too could walk invisible.

So, to finish off this story, read Shakespeare's Henry IV, act 2, scene 1, lines 95-98, written in 1597. One of the characters says "...we have the receipt of fern seed, we walk invisible."