Tree ferns fascinate me. We had ferns in our yard in New York and again in Georgia. They were nice orderly plants and kept to the shade, never growing taller than a meter or so. Then we moved to the tropics and the strangeness began. What strangeness?
First of all, ferns do not have trunks (they just don’t) and here these ferns were growing out of the top of an actual trunk. Hmm. Then there was their age. Tree ferns, actually all ferns, were around when the dinosaurs were alive. They are old. Then I found out about their reproductive habits, the very private life of ferns, and it is very strange.
Today, we are used to vascular plants that use flowers to attract pollinators like bees, ants and butterflies. The plants flower are pollinated and produce seeds. We know that some trees need cross-pollination. There must be a boy tree and a girl tree or there will be no baby trees. Fair enough. Then there are trees that have male and female parts in one tree. You have one tree and it can have baby trees. All this seems normal. Then come the ferns.
Ferns are not like “normal” vascular plants like the apple. Ferns don’t make flowers for busy bees. They make spore sacks under their fronds (they are too ancient to have leaves). From the sacks come spores, and I always believed that the spores just made baby ferns (I thought I understood biology. Oh, the embarrassment). Spores don’t make ferns. They make gametophytes, a platform of sorts that is a kind of intermediate stage of development. When they are mature, gametophytes, which are hermaphroditic, make eggs and sperm.
Given the right conditions (especially moisture), the eggs and sperm get together on the gametophyte (think tiny little waterbed) to make an embryonic fern. This little fern has two parts, a shoot that grows up toward the sun, and a root, that embeds itself in the gametophyte to stabilize the shoot. With a gametophyte the size of a dime and a lot of eggs and sperm floating around, there is intense competition for survival. Something does survive, of course, and grows up to be just like the parent plant.
So there you have the very private life of ferns. I have never seen a gametophyte. But, just in case, I am making some very tiny sheets for water beds. You never know.