Is this an Acanthocereus tetragonus or subinermis?

[valerie7686]

Hi all! First time poster here! I now live in south Florida now and was overjoyed to find this beauty in my yard when I moved in. I believed it to be an Acanthocereus tetragonus until recently. I know they are native to this area and, to my eye, all characteristics seemed to match. Recently another cacti lover familiar with native Florida species suggested that it was an Acanthocereus subinermis, native to Mexico. I was unable to find much information on this species but would love to hear any insight anyone could provide. It is a relatively fast grower and blooms throughout the summer for one night only. Thank you in advance

[Lucy_V]

according to Britton & Rose (First published in Cact. 2: 125 (1920) Acanthocereus subinermis is a synonym of Acanthocereus tetragonus

[valerie7686]

Thank you for the response! That makes sense! Any pictures of "subinermis" look exactly the same as the tetragonus (to me anyway) although the few places that had any information had slightly different descriptions. But the tetragonus is highly variable anyway so I was wondering if the description differences reflected that. I appreciate your post!

[anttisepp]

Many thanks for your post and picture. Maybe it will become clear to those who think that "Fairy Castle" is a cultivar of Acanthocereus tetragonus.
Sad mistake of some non-educated commercial gave subsequence of wide misunderstanding.

[oneday]

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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[valerie7686]

I love that we are on the quest together here! I agree that my big cactus looks more like the first three photos you posted (A. subinermis). Some of the younger ones are thinner with larger barbs and actually look just like the last photo too though!

I am still on the hunt for a proper A. tetragonus to see the differences myself! I have had the google maps of the site you suggested open on a tab for the next day I'm free I would be especially interested to see the blooms if you are able to get any photos of that.

UF has a plant identification service that I have been looking into so I may try that next to get more info. I'll be sure to update here if I do!

Thank you for your thorough post!

[DaveW]

Excellent researched post on the subject Oneday.

Inermis means unarmed or spineless, therefore subinermis means almost spineless or less spiny? Of course botanical names do not have to be appropriate and later often aren't, but usually are when the species was described.

Britton and Rose pictures show the difference for a spiny A. tetragonus (syn A. pentagonus) and the short spined A. subinermis. Also Oneday's other pictures illustrate this fact.

[oneday]

The meaning of the name is interesting, never looked it up. That does seem to fit, subinermis does seem to have shorter spines in general, that's what got me wondering in the first place. According to the Britton & Rose it can be completely absent of spines, though I have not seen that in the individuals here.