We No Longer Understand Ferns

Some things are hard to understand - for example tomatoes are botanically fruit but culinarily vegetables. Apparently, ferns make that list.

That's right! If you didn't think that that alien looking frond-containing green plant-like thing is already strange, today you're going to learn that ferns are weird for reasons other than their appearance. Well, another weird thing about them is their reproduction - they don't have seeds nor flowers and instead reproduce via spores like some sort of weird fungus. Ferns should be at the top of your "odd lifeform" list if for nothing else but the fact that the adder's tongue fern has the most chromosomes of all multicellular organisms. This particular fern has about 720 pairs of chromosomes and for reference, people on average have 23.

That isn't even the strangest thing about ferns. Scientists sequenced the massive genomes of 3 different homosporous ferns and found that in addition to having an almost comically large genome, ferns are also stealing DNA from other organisms. How much DNA was there? 7.46 gigabases of DNA - more than twice that of the human genome - in one fern containing 39 chromosomes. The scary thing is that according to our fossil records, ferns haven't changed much over the last hundred million years, making them the "alligator" of the plant kingdom.

The real question here is - what are they hoarding all of that DNA for? A partial answer was found in a separate species of fern where its genome had a genetic defense mechanism that is believed to be stolen from bacteria in order to protect it from a specific toxin. Clearly, some of the "extra" DNA is from other organisms and has been retained to help the fern survive. In addition, instead of having the expected massive segments of repeated sections (something that a lot of DNA has to avoid error during replication) there were large sections that didn't quite fit with what is expected to be seen with a plant let alone a fern.

To be clear, repeated DNA segments are common in most organisms, but for plants specifically it is not unusual to see large repeated sequences to help preserve their functional DNA when their cells replicate. Those sections were repeatedly seen and are unexpected in this case for two reasons, the first being that usually organisms will shed the unnecessary repeats to keep them at a more "manageable" level, but ferns appear to have stopped doing that at some point long ago. As it turns out, ferns are the plant version of "if it isn't broken, don't fix it."