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My research on the matter can be summarized in a sentence: "It [sporangium] can be composed of a single cell or can be multicellular" (Source: https://en.wikipedia.org/wiki/Sporangium). Yet there shouldn't be a reply placed between "They are" and "They aren't" test options, speaking of "Are bryophyte sporangia multicellular?". A link to the source where I could ascertain whether the bryophyte sporangia is multicellular (if I could ascertain) is highly appreciated.

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In Embryophyta (land plants), including bryophytes, the sporangium is usually a multicellular structure.

Life cycle of a hornwort. The dehisced sporangium is shown releasing spores and elaters.

Perhaps you meant to ask about the number of spore mother cells (SMCs) in each sporangium? That varies across groups. In bryophytes, each sporangium has many SMCs, and accordingly produces a large number of spores. (Contrast this with angiosperms, where a megasporangium [called an ovule] has only one megaspore mother cell.)

References and further reading:

  1. https://courses.lumenlearning.com/boundless-biology/chapter/bryophytes/

  2. https://www.britannica.com/science/plant-development

Image attribution:

By LadyofHats. (Public domain; https://commons.wikimedia.org/wiki/File:Hornwort_structures.jpg)

Adhish
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  • Thanks! Referring also to the "Great Soviet Encyclopedia" 3rd edition (1970-1979), in particular, a sporangium is multicellular in higher plants. Now, scarcely do I understand why a sporangium of angiosperms is multicellular if it has a single megaspore mother cell. Is this because of four megaspores - the daughter cells in the process of meiosis in a megaspore mother cell? –  Sep 09 '20 at 03:28
  • @Lesya It is multicellular because it has cells OTHER THAN the megaspore mother cell (and its derivatives): namely the nucellus. See https://botit.botany.wisc.edu/botany_130/diversity/plants/Vascular_Plants/Magnoliophyta/Angiosperms/ovule-labelled.html. – Adhish Sep 09 '20 at 12:43