I've seen a lot of information lately about intestinal flora or gut flora but I was under the impression that flora refers exclusively to plant life. So how did bacteria come to be called flora? I am aware that they aren't really animals either, but naming them after plant life seems... wrong.

To confuse matters further, aquariums often suffer from a condition called bacterial blooming which has nothing to do with flowers.

P.S. There is indeed a Yahoo Answers! post about this topic, but it would be nice to have a more language-based discussion.

  • 5
    Bacteria are neither plants nor animals. Come to that, fungi and algae aren't plants either, but I bet you don't think there's anything odd about lumping them in with flora. I just think of flora as everything alive that's not fauna. It's just that the more noticeable flora are plants, and most of us get a bit vague when it comes to classifying, say, yeast or viruses. Commented Nov 12, 2011 at 4:29
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    They aren't named after plants. I think the problem is that your impression is that flora means plants. Once you get around that problem it is a lot clearer:-)
    – Rory Alsop
    Commented Nov 12, 2011 at 10:08
  • 1
    Gasp! You mean Wikipedia is wrong?
    – saritonin
    Commented Nov 12, 2011 at 14:05

3 Answers 3


If you look at the entry for flora at dictionary.com you can see:

flora noun — 4. the aggregate of bacteria, fungi, and other microorganisms normally occurring on or in the bodies of humans and other animals: intestinal flora.

Furthermore, if you look at the entry at etymonline you can see this:

extended form of *bhel- (3) "to thrive, bloom,"

Which is talking about the PIE root. It seems appropriate to use flora to refer to fungi, bacteria, algae, etc., because they all bloom and *bhel- is the origin of the word bloom.

English speaking scientists will often take words from English, especially ones with a Latin or a Greek base, and use them for what seems appropriate at the time. Sometimes the scientific meaning comes back into the mainstream. E.g. orbit, torus, virus, etc.

  • Also, not to be confused with flora and fauna. Another meaning.
    – Lambie
    Commented Nov 13, 2023 at 18:02

FumbleFingers has it wrong: Algae ARE plants! If you want to dispute this, you'll have to tell me the taxonomic kingdom to which they're assigned that's other than Plantae. Fungi also were formerly classified in Plantae but they've gotten their own kingdom, namely Fungi, sometime since when I first learned about taxonomy many decades ago.

I've read that the organisms in the gut microbiome being collectively termed "flora" goes back to the era when everything was classified as animal, vegetable, or mineral. I'm not sure I believe that, but bacteria have also been lumped in with plants at points in the past. Nowadays, like the fungi, they have their own kingdom which is Monera. But in the classification systems accepted in some parts of the world, bacteria have been divided into two different kingdoms, those being Archaebacteria and Eubacteria, with Kingdom Monera thrown in the trash heap.

I'm kind of glad that I'm heading into my mid-60s and probably won't be around to see AI get its evil clutches onto taxonomy, or at least I really won't care!


I think it is a case of mistranslation or misinterpretation that got to stick.

What has always struck me personally was "gut flora". I know that "flora" is plants (flower) and fauna is animals. Biome seems a more adequate term to use, as bacteria is neither plant nor animal, that is "a community of biological life inhabiting a specific environment". In fact, the terminology for microorganisms that dwell on or in the human is known as human microbiota.

In short, as I mentioned, one of the many cases of fallacies that got to stick. Like calling Native Americans "Indians", or "begging the question", there are many others too, especially in layman modern day language.

The wikipedia article linked above confirms my initial suspicion was correct:

Though widely known as flora or microflora, this is a misnomer in technical terms, since the word root flora pertains to plants, and biota refers to the total collection of organisms in a particular ecosystem. Recently, the more appropriate term microbiota is applied, though its use has not eclipsed the entrenched use and recognition of flora with regard to bacteria and other microorganisms. Both terms are being used in different literature.

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