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Approximately, how many families have been identified?

I've often often come across figures for the total number of species on Earth. Recently, I found myself wondering about the encompassing ranks above them, specifically family, but I can't recall any figures on family and it's a little difficult finding what I want by typing "family" into a Google search. ;)

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Families (and really, any taxa except species, to some extent) are artificial, fluid and ever-changing. That's not to say they aren't useful, but the number of families is likely to be changing quite a lot on a nearly daily basis, as more and more families are converted into monophyletic groups based on DNA evidence. –  Chinmay Kanchi Feb 6 '14 at 21:12
... but just as a round estimate its thousands at least. browsing encyclopedia of life I see scores just in the flowering plants... –  shigeta Feb 9 '14 at 6:15

3 Answers 3

The NCBI Taxonomy statistics page displays the following information:

There are currently 73540 genera, 331418 species, and 23127 taxa of higher order. Since the number of taxa decreases with the genericity of the taxon, there are probably around 20000 families, give or take a few thousand.

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I don't know about other groups, but about plants, number of families depends on the system you follow. Recent version of The Plant List (1.1) estimates about 352 000 species of Angiosperms and lists over 400 families. See It is very good and reliable source of information. Second very good source about plant systematics is database Tropicos provided by Missouri Botanical Garden and Angiosperm Phylogeny Group. See list of families according to APG3 and click to "Families" on the top of the page. Just note, that there are also synonyms, so that You can't just count the rows. ;-)

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The Plant List has 642 families listed:

For a quick comparison, Wikipedia lists

  • 522 fish families:
  • 136 mammal families:
  • 61 amphibian families:
  • 57 reptile families:

This only covers a subset of the total, however (see here for other animal classes). It is relatively difficult to find a good, and relatively complete answer to this, though.

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