Hi, I am the commentator on the OP's video - I've done a bit more research on this niche cactus nerd topic since then
I am became interested in the topic because I have a cactus similar to the OP in my yard, and for a while I thought it was A. tetragonus as well as it is sometimes labeled as that. It's fairly common in the South Florida area in people's yard and escaping into suitable neighboring natural areas. Then I started seeing some wild, habitat restoration, and some nursery cacti represented as the native (to Florida) A. tetragonus, and I thought I must not actually have the same species. That's where the rabbit hole began.
The 1920 Britton & Rose book is where I believe the first delineation is found, they recognize, among other Acanthocereus spp., an A. subinermis and an A. pentagonus. The A. pentagonus is actually the synonym for the current A. tetragonus, the wide ranging species that is native to coastal South Florida among other places. A. subinermis is said to be from Mexico. I've attached the illustration from that book showing the two species, and here's a link to the full PDF, I believe it's in the public domain -
https://drive.google.com/file/d/1KEmCQV ... share_link
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Here is also a recent paper from a Mexican university which does a deep dive on A. tetragonus and A. subinermis, stating the A. subinermis is a Mexican endemic species while A. tetragonus is the wide ranging species that is native to South Florida as well. It's primarily geared towards using both as a food source (conclusion: the young stems and fruits of both are good eatin'), and it's in Spanish but there is some interesting maps and discussion on the distribution of both, A. tetragonus is found mainly in coastal regions, while A. subinermis is more inland and found at higher elevations.
https://drive.google.com/file/d/1QmBvc4 ... share_link
Where it gets confusing is that A. subinermis has been declared a synonym for A. tetragonus by Plants of the World Online, here -
https://powo.science.kew.org/taxon/urn: ... mes:1645-2. Here they list one authority that has declared this, but list three other authorities that have recently maintained that A. subinermis is a separate species.
Probably it would some further studies with molecular analysis by biologists to properly place A. subinermis, whether it is in fact a species, subspecies, or just a local variant of A. tetragonus, but in my head taxonomy there is certainly some difference, I can instantly recognize one or the other based on the stems (I haven't seen much of the flowers yet).
Here's some pics of a containerized A. subinermis that was labeled as such at a local nursery and some I've found growing in (or out of) people's yards, I believe the OP's is this type, and that all instances like this are not Florida native lineages, they were imported from Mexico, probably because growing this type over the native variety was more profitable:
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In contrast, here's a A. tetragonus that was labeled as such at the same nursery, in the "Florida native cacti" section - I bought it and planted it my yard, I enjoy both of them! Also, some pics of the a large native one at John Pennekamp, and one I found in the "Coastal keys habitat" section in Fairchild Botanical Garden in Miami, FL:
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