Behold! The most complex creature in all of creation!

Bow down before the organism God actually created in his own image: a small fern found on New Caledonia, Tmesipteris oblanceolata. Furthermore, the name of God’s avatar is also unpronounceable.

Tmesipteris oblanceolata

160 billion base pairs! Our genome has only 2% of the complexity of this fern.

We need to make a pilgrimage to a small island east of Australia now.


  1. Matt G says

    All I said was “that piece of halibut was good enough for Tmesipteris oblanceolata.”

  2. F.O. says

    Apologies in advance for the utter ignorance of biology.
    Doesn’t at some point having that much DNA to lug around and copy and transcribe get in the way of doing things efficiently?
    Doesn’t the amount of DNA affect metabolism in some way?

  3. says

    random hypothesizin’ time, my turn: there was a very unusual survival benefit for having a fat slug of chemicals in the middle of your nucleus for this fern at some point, like maybe a DNA-gobbling bacteria evolved and this was their quick-and-dirty solution. who’s next?

  4. Reginald Selkirk says

    Doesn’t at some point having that much DNA to lug around and copy and transcribe get in the way of doing things efficiently?

    It’s a plant. It doesn’t “lug around” anything.
    It only needs to be copied during cell division. Yes, this is a cost, but the penalty is not so much as you might think.
    Most of it doesn’t need to be transcribed. A small amount will be anyway, see the previous point.
    Since it’s mostly just sitting there, it has little effect on efficiency.

    Recommended reading: What’s in Your Genome?: 90% of Your Genome Is Junk
    by Larry Moran, ISBN: 9781487508593

  5. keinsignal says

    Hey, so, off-topic but I wanted to share that Robert Evans’ “Behind the Bastards” podcast just dropped part one of a series on Kent Hovind. I’m looking forward to learning a whole new set of reasons to be disgusted by this weird-ass charlatan!

    Cool fern btw.

  6. John Morales says


    “The largest living fungus may be a honey fungus[25] of the species Armillaria ostoyae.[26] A mushroom of this type in the Malheur National Forest in the Blue Mountains of eastern Oregon, U.S. was found to be the largest fungal colony in the world, spanning 8.9 km2 (2,200 acres) of area.[27][28] This organism is estimated to be 2,400 years old.”


  7. ardipithecus says

    It’s my understanding that plants generally have larger genomes than animals. My first guess as to why is that plants don’t have a nervous system so they have to do all that with chemical messaging. They need thousands of messengers while animals only need 100 or so. That’s a lot of synthesis to be managed.

  8. consciousness razor says

    Just give it to me straight for once, PZ. Do I have to work for big brainstem™ now or what?

  9. nomdeplume says

    Should, but won’t, put an end to the “DNA is a code” nonsense from creationists.

  10. Hemidactylus says

    It’s not surprising at all that Carl Zimmer didn’t shit on himself conveying this. He says:

    There are two chief ways in which genomes expand over evolutionary time. Many species carry virus-like stretches of DNA. As they make new copies of their genomes, they sometimes accidentally make an extra copy of that viral stretch. Over many generations, a species can accumulate thousands of new copies, causing its genome to swell.

    It’s also possible for a species to suddenly end up with two genomes instead of one. One way for an extra genome can arise is for two closely related species to mate. Their hybrid offspring may inherit full sets of DNA from both parents.

    Dr. Pellicer and his colleagues suspect that a combination of virus-like DNA and duplicated genomes is responsible for the huge amount of genetic material in Tmesipteris oblanceolata. But they don’t know why this humble fern ended up with a record-setting genome while other species — like us — have so much less DNA.

    I’m no expert on this stuff but I’d lean heavily into the ploidy angle myself. Would viral sequences accumulate to that degree? Of course how often do viral sequences confer any benefit to an organism aside from maybe placentation in mammals thanks to an inserted retroviral sequence?

    With ploidy as with gene duplication there may be benefits with added genes producing more gene product. Human liver cells can be polyploid, but to what known benefit?

    Adding copies of genes via duplication in meiosis cross-overs or by full genome ploidy could allow copies to diverge in function (cue Susumu Ohno), but just as well might result in the copies degenerating into nonsense, as my reply is kinda doing at this point.

    So maybe polyploid plants have a bunch of decayed former genes if the addition of copies adds nothing beyond initial sufficiency?

    I really don’t know if this speculation by Zimmer is warranted:

    Eventually, however, genomes may get so big that they become a burden. Cells may have to expand to house all the extra DNA. They also need more time and more nutrients to make new copies of their giant genomes. An organism with an oversized genome may lose out to a rival with a smaller one. So mutations that chop out unneeded DNA may be favored by evolution.

    Also this part leads me to another important concept left out:

    In the early 2000s, when Dr. Pellicer trained as a botanist, he was intrigued to learn that a few lineages of plants have massive genomes as well. Onions, for example, have a genome five times as large as ours.

    The onion test?

  11. Hemidactylus says

    Reginald Selkirk @6
    Didn’t PZ say he was going to review Moran’s book at some point…?

  12. Hemidactylus says

    Also a bit off piste for the current topic but isn’t polyploidy a means for plants to undergo instantaneous (dare I say saltational) speciation? A rediscoverer of Mendel Hugo de Vries was smitten by a primrose. I tried skimming this but my post-work brain started glitching:

    One of the most important problems in evolutionary biology is to understand how new species are generated in nature. In the past, it was difficult to study this problem because our lifetime is too short to observe the entire process of speciation. In recent years, however, molecular and genomic techniques have been developed for identifying and studying the genes involved in speciation. Using these techniques, many investigators have already obtained new findings. At present, however, the results obtained are complex and quite confusing. We have therefore attempted to understand these findings coherently with a historical perspective and clarify the roles of mutation and natural selection in speciation. We have first indicated that the root of the currently burgeoning field of plant genomics goes back to Hugo de Vries, who proposed the mutation theory of evolution more than a century ago and that he unknowingly found the importance of polyploidy and chromosomal rearrangements in plant speciation. We have then shown that the currently popular Dobzhansky–Muller model of evolution of reproductive isolation is only one of many possible mechanisms. Some of them are Oka’s model of duplicate gene mutations, multiallelic speciation, mutation-rescue model, segregation-distorter gene model, heterochromatin-associated speciation, single-locus model, etc. The occurrence of speciation also depends on the reproductive system, population size, bottleneck effects, and environmental factors, such as temperature and day length. Some authors emphasized the importance of natural selection to speed up speciation, but mutation is crucial in speciation because reproductive barriers cannot be generated without mutations.

  13. Reginald Selkirk says

    @13: I’m no expert on this stuff but I’d lean heavily into the ploidy angle myself. Would viral sequences accumulate to that degree? Of course how often do viral sequences confer any benefit to an organism aside from maybe placentation in mammals thanks to an inserted retroviral sequence?

    If one includes both transposons and viruses as “virus-like stretches”, the answer is: yes, they really would accumulate.
    What’s in your genome by L. Moran
    This is a brief table of what is in the human genome. Transposons 44%, viruses 9%, and a very small fraction of those are active. In fact, about 10% of the human genome is made up of one family of repetitive sequences (which Moran would classify as transposons, or transposon-like) Alu, with about a million copies.

    I really don’t know if this speculation by Zimmer is warranted: …

    You probably noticed that he uses a lot of waffle words, “may” this, “may” that. A lengthier discussion would include mention of the nearly-neutral theory of evolution.

    Onions, for example, have a genome five times as large as ours…

    The onion test?

    Yes, the onion test. Perhaps more interesting than the human::onion comparison is the variation in genome size between species of onion (wikipedia) which do not appear much different.

    Plants do seem to be more prone to polyploidy than animals, but humans – and other vertebrates have evidence of two whole genome duplications deep in the past.

  14. Tethys says

    Polyploidy is most common in plants, though salamanders and leeches are animals that exhibit polyploidy. It is often linked with the ability to reproduce asexually.

    Only a small proportion of the plants have been sequenced, but ferns and mosses evolved early in the history of Earth so I wouldn’t be surprised if many species display such enormous genomes.

  15. says

    I wonder how its amount of DNA compares to another fern, Ophioglossum reticulatum, which at a haploid number of 1260 – 1500, holds the record among plants for most chromosomes?

  16. Hemidactylus says

    Reginald Selkirk @16
    Yeah good point about tranposons and Alu in humans.

    I still wonder to what extent ploidy itself contributed to the genome size of this ferm versus viral sequence accumulation. Here’s the original article:

    This organism is at 160.45 Gbp/1C. They say:

    Tmesipteris (Psilotaceae) is a relatively understudied small genus made up of ∼15 species,12 which are mainly epiphytic ferns occurring in Oceania and several Pacific Islands. Until now, the genome sizes of only two species had been reported in the genus, i.e., for the tetraploid T. tannensis (1C = 73.19 Gbp13) and the octoploid T. obliqua (1C =147.29 Gbp9), both with giant genomes, and with the only two known ploidy levels reported for the genus (based on x = 5214)

    So the octoploid above is 2.01 times larger in genome than the tetraploid which seems a doubling of ploidy equalling a doubling of genome size. T. oblanceolata subsp. linearifolia is 2.19 times larger than T. tannensis above in genome size. Ploidy still seems important.

    They say:

    Tmesipteris oblanceolata subsp. linearifolia has been reported, like P. japonica, to be an octoploid, but it has a much higher chromosome number (2n = 416 versus 2n = 407,19). Its massive genome is thus considered to have arisen through the combined effects of repetitive DNA accumulation and polyploidy, as in other species of the genus.20

    I see Joe Felsenstein is here so I defer to him on the details.


    However, unlike angiosperms where polyploidy is also prevalent,17 post-polyploid diploidization mechanisms in ferns typically involves gene silencing without significant DNA elimination, resulting in high chromosome numbers but reflecting a diploid-like gene expression.18

    I wonder over time if the gene copies would decay away from being functional sequences.

  17. chrislawson says

    F.O.@4 — the metabolic cost of DNA replication and storage is surprisingly small. This is one of the reasons antibiotic resistance is such a big problem. I remember being taught at uni (back in the Pleistocene) that if we stopped exposing bacteria to antibiotics they would quickly lose their resistance because of the reproductive advantage of not having to copy all that DNA. We now know that bacteria will happily hold onto their resistance plasmids for many, many generations even when they are not exposed to antibiotics. Preventing antibiotic exposure does help, but only because those resistance genes eventually mutate to become ineffective in the absence of selection pressure — a far slower process than being actively selected against, while allowing quick recovery of functionality with a few point mutations if antibiotic exposure resumes.

    Hemidactylus@13– Echoing Reginal Selkirk here: roughly half the human genome is viral remnants or repetitive sequences that we suspect are of viral origin.

  18. chrislawson says

    Adding to the comment above: When there is a polyploidy event, viral remnants will be duplicated along with the rest of the chromosome. Polyploidy and viral inclusion are not mutually exclusive processes.

  19. Hemidactylus says

    chrislawson @20 and @21
    Yeah I was more focused on plant ploidy than the case in humans but see your point about ploidy actually multiplying the extent of existing viral remnants.

    As for antibiotic resistance with plasmids and also to some extent phages bacteria pretty much excel at file sharing (prokaryotic Napster) so a horizontal gene transfer sort of gene flow is happening. If bacteria lose antibiotic resistance it might not be a big deal to borrow it from another type of bacteria in the future. I guess this could be compared also to crowd sourcing.

  20. KG says

    check out the crows when you are visiting! – Robbo@2

    In New Caledonia, the crows check you out!

  21. John Harshman says

    @Hemidactulus #13:

    Adding copies of genes via duplication in meiosis cross-overs or by full genome ploidy could allow copies to diverge in function (cue Susumu Ohno), but just as well might result in the copies degenerating into nonsense

    That has a name: diploidization. Duplicate chromosomes diverge, by selection or drift, until it’s hard to tell that they’re homologous.

  22. UnknownEric the Apostate says

    I believe New Caledonia is also where crested geckos originate, so if we all go, I’ll have to bring my daughter’s gecko Alex so he can visit his homeland. :)

  23. Kagehi says

    @4 FO

    As most others have said, with one caveat – There are cases in which microbes have shed nearly all excess DNA, but this is in environments with massively low levels of available energy, and I think also usually oxygen poor ones. This is due to the fact that they can’t a) get food quickly and efficiently, and b) non-oxygen based metabolic processes, while they work, are themselves less efficient, so such organisms need to conserve energy in all things that they do. Something like this plant though… has basically more than it needs from the soil and sunlight to replicate pretty much any amount of DNA it wants, with, as has been said before, almost no constraint on the costs.

    On an aside, and as a joke, its an Australian plant, so obviously all that extra DNA must be there to provide it with new ways to try to kill us in the future, when all the other terrible things on that continent fail! lol

  24. Silentbob says

    From the link in the OP:

    “A lot of biology is ‘why not?’ rather than ‘why?’” said Julie Blommaert, a genomicist at the New Zealand Institute for Plant and Food Research who was not involved in the new study.

    Yes. Much of science seems to be reorientating in this way. Cosmologists used to say, “why is there something rather than nothing”? Now it’s more, “why would there be nothing”?

    Likewise in biology it’s becoming less a question of why a thing should exist, and more a question of why it should not.

  25. Hemidactylus says

    John Harshman @24
    Thanks! That tidbit of info may help me figure out a bit more what may be going on with this fern! Plus it adds to my ongoing education on these fascinating issues.

  26. Hemidactylus says

    Cool stuff:

    Clearly a case of confirmation bias on my part as the wiki shows diploidization has got more moving parts than this yet:

    Relaxed selective pressure on duplicated genes
    The duplicated copies of a gene are commonly non-essential to the plant’s ability to maintain normal growth and development. Therefore, one copy is generally free to mutate/be lost from the genome.[2][4] This contributes to gene loss through the massive chromosome reorganization events during genome shock.

    As mentioned earlier, duplicated genes are under relaxed selective pressure. Thus it may also be subject to neofunctionalization, the process in which a duplicated gene obtains a novel function.

  27. seachange says

    New Caledonia is undergoing political violence right now. Hope this poor fern survives.

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