Field of Science

Is the plural Calyptrae or Calyptras?

The moss calyptra is a small cap of gametophyte tissue that covers the apex of the moss sporophyte during its development. This little structure was the focus of my dissertation. Below is part of a figure that I used in my defense showing calyptra from several different moss species. The calyptrae are indicated by the orange arrows

This discussion may seem (ok) is pretty esoteric, but a reviewer on my last manuscript brought up this question. They proposed using calyptras as the plural of calyptra, rather than calyptrae. (Yes, these are the things that I think about for my job.)

This is part of the reviewer response that I sent to the editors regarding this question.
We agree that there are challenges when adopting terms into other languages especially concerning the plural form of the word. The term calyptra is derived from the Greek word kalyptra, meaning veil or hood. The plural for the Greek word kalyptra is kalyptrai. However, with the change in spelling and its use in other languages the term has been latinized. Often Greek plurals ending in –ai are transformed into –ae (e.g., mycorrhizae, cypselae, thecae). Perhaps this was originally a spelling error, but at least in terms of the moss calyptra the –ae ending has persisted. In the two most widely used bryological glossaries (see references below) the plural form is cited as calyptrae and many papers and books use this plural form. I do not think that retaining this traditionally used plural form makes the study any less accessible to non-bryologists as there are other botanical terms that have similar plural forms. Thus, we would prefer to continue to use calyptrae as the plural form in our manuscript. Additionally, switching to an –s ending would require additional explanation, which is outside of the manuscript’s focus.
Thanks to my colleague Nic Tippery who contributed to this explanation and I consult on all words Greek and Latin.


  1. The transformation to -ae isn't a spelling error as such. Many Greek words carried into English came via Latin, and they've been adjusted slightly to match Latin grammar. Another example of this is how we refer to 'hippopotamus' and 'hippopotami' rather than 'hippopotamos' and 'hippopotamoi' (the Greek masculine ending -os has been adjusted to its Latin equivalent -us).

  2. Good point Christopher. I went back to Nic's messages and he had mentioned the transformation via Latin too. Apologies for the incorrect statement and thanks for keeping my info accurate.

  3. Thanks for the shout-out, Dr. Budke. Below is a link that might interest you:

    ... in case you become subversive later in life and need to get your point across.

    1. Hey Dr. Tippery,
      I have seen the moss graffiti instructions before, but have yet to try it myself at home. I feel like I do plenty of moss growing in the lab and maybe too much so to bring it home. I think that the graphics on this website are particularly well done. It may be time for a subversive graffiti post!
      I hope that all is well,


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