I have a friend who likes to promote hemp on Facebook, and one of the posts had this "factoid":

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Looks highly doubtful to me but I can't find any real supporting/disputing info.

Is there anything that would support/refute this claim?

Best I can find that even remotely tries to use real data is https://comebackdaily.co/how-is-hemp-even-better-than-trees-for-producing-oxygen/

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    Note that there is no shortage of oxygen, so although academically interesting, it has little to no practical implication if true. The claim probably seeks to imply that the additional oxygen production is advantageous, even if not stated.
    – gerrit
    Jul 21 '20 at 9:00
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    I made a number of improvements to your question. You have reversed them. I guess we need to go through each one one-by-one until we can knock this question into shape.
    – Oddthinking
    Jul 21 '20 at 16:35
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    You use the word "factoid" in quotes. A lot of people don't seem to know that that word implies it is false. Hence you are prejudging the answer without evidence. I suggest you remove that word.
    – Oddthinking
    Jul 21 '20 at 16:35
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    You link to ComebackDaily. Your link is a raw URL. I suggest you inline it to make it more readable, and more clear why you might click on it.
    – Oddthinking
    Jul 21 '20 at 16:36
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    You claim that Comeback Daily (remotely) tries to use real evidence. It isn't at all clear why you say that. You should quote the relevant sections that do what you claim.
    – Oddthinking
    Jul 21 '20 at 16:38

Comback Daily argues that with two crops per year and with more efficient C4 photosynthesis ...

The claim is based on the false premise that Cannabis species use C4 photosynthesis.

Several of the grasses use C4 photosynthesis. Despite its nickname, Cannabis species are not members of the grass family. They are members of the Cannabaceae family, all of which use C3 photosynthesis (the same mechanism used by most trees). No member of the Cannabaceae family is listed in a very extensive list of C4 plants [Sage], and the photosynthesis in Cannabis sativa is consistent with C3 photosynthesis rather than C4 photosynthesis [Chandra].


Chandra, Suman, et al. "Photosynthetic response of Cannabis sativa L., an important medicinal plant, to elevated levels of CO 2." Physiology and Molecular Biology of Plants 17.3 (2011): 291-295.

Sage, Rowan F. "A portrait of the C4 photosynthetic family on the 50th anniversary of its discovery: species number, evolutionary lineages, and Hall of Fame." Journal of Experimental Botany 68.2 (2017): e11-e28.

  • I also found several reddit and quora posts that claimed that cannabis species use C3 photosynthesis, but those are not credible sites. The few sites that I did find that claim that cannabis species do indeed use C4 photosynthesis are all non-credible sites, and the claims therein are unreferenced. Jul 21 '20 at 13:22
  • This unfortunately wasn't my question; one of the mods edited my question to something with a different intent focused on the article I linked to.
    – Jason S
    Jul 21 '20 at 14:22
  • @JasonS -- This does answer your question; you just don't know it. Oddthinking picked out the key claim (which is false) that underlies the claim that an acre of hemp produces more oxygen than 25 acres of forest. That claim, buried in the combackdaily.co article, is that hemp uses C4 photosynthesis. I suggest you reverse your reversal. Jul 21 '20 at 14:59
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    This picks one feature of the argument apart, but not really the relativist aspect of real world data comparison in the claim. If hemp and tree are both C3, we still would like to know how 1 hectare of each produces how much O2? Jul 21 '20 at 16:07

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