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Good day all. I am looking for some help in pegging this one down. It was just added to my collection, and I suspect it is a fairly common plant.
I cannot however, seem to find anything that looks obvious when looking through my "The Cactus Family' reference book.
Any thoughts would be appreciated. Thank you.

Gymnocalycium denudatum, I would think.

Gymocalcium horstii is also viable.

As far as I know the easiest way to tell the two apart is the orientation of the spines. G. horstii spines tend to point away from the stem at reasonable angles, whereas G. denudatum has spines pressed more or less against the stem. This plant fits G. denudatum better in my opinion.

http://www.cactus-art.biz/schede/GYMNOC ... udatus.htm
You really sure? You might have meant
Gymnocalycium buenekeri
http://www.cactus-art.biz/schede/GYMNOC ... nekeri.htm

stefan m. wrote:http://www.cactus-art.biz/schede/GYMNOC ... udatus.htm
You really sure? You might have meant
Gymnocalycium buenekeri
http://www.cactus-art.biz/schede/GYMNOC ... nekeri.htm

cactus-art.biz is not a particularly trustworthy site for taxonomic issues like this. G. horstii ssp. horstii has a glossy epidermis, in contrast to G. buenekeri (G. horstii ssp. buenekeri). G. horstii and G. buenekeri both should be rounder and have spines less pressed against the stem, as compared to G. denudatum. The plant here looks like G. denudatum to me, though I do not know the extent of hybridization of these taxa in cultivation.

"G. denudatum to me, though I do not know the extent of hybridization of these taxa in cultivation."
Bear in mind the owner live in nova scotia- so in all likelyhood a plant of that age and size is from a wholesale nursery- and that a lot of these requests are wholesale plants that have been hybridized like you just stated. G. dedudatum when looked up, either get the plant from cactus-art, or ones similar to G.horstii and relatives. So, bear in mind im not saying this with 100% certainty, that labeling a no ID plant with a species with ID issues of its own is pretty much why cereus "peruvianus" became a "species" in the first place.

Cereus peruvianus never became a valid species. It is published as cereus hildmannianus.
And the so called cereus forbesii that has the common monstrose and spiral forms is published as cereus hankeanus.
Old names just won't disappear

I never said it is. I did add quotation marks. Cereus hildamanius is often too spiny.

stefan m. wrote:"G. denudatum to me, though I do not know the extent of hybridization of these taxa in cultivation."
Bear in mind the owner live in nova scotia- so in all likelyhood a plant of that age and size is from a wholesale nursery- and that a lot of these requests are wholesale plants that have been hybridized like you just stated. G. dedudatum when looked up, either get the plant from cactus-art, or ones similar to G.horstii and relatives. So, bear in mind im not saying this with 100% certainty, that labeling a no ID plant with a species with ID issues of its own is pretty much why cereus "peruvianus" became a "species" in the first place.

You offered a species-level ID yourself, so I do not see what the issue is with me doing so. The issue of Cereus hildmannianus synonyms has nothing to do with this. These Gymnocalycium species are supported based on field studies and the latest phylogeny. Going on Google pictures for morphologically similar species such as these is a bad idea.

Arent cacti contstantly reclassified anyway? Why apply rules for cacti in that grow in the wild, when the specimen originates from wholesale?
Is anybody even studying wholesale plants? I dont recall someone doing so recently.

stefan m. wrote:Arent cacti contstantly reclassified anyway? Why apply rules for cacti in that grow in the wild, when the specimen originates from wholesale?
Is anybody even studying wholesale plants? I dont recall someone doing so recently.

You'll have to find someone else to argue for the sake of arguing. You're not saying anything productive at this point.

No doubt there are hybrids in cultivation Stefan, but many of us try and avoid them by getting our plants from reliable sources, either as plants or seed.

G. denudatum and horstii are easily separable on flower colour from var buneckeri, since the former have white flowers whilst v. bueneckeri has pink ones.

As MD says G. denudatum, due to its spines closely adpressing the body and looking like a spider on the plant used to be known as the "spider cactus". G. horstii however has mostly straight spines, some or all of which, project out from the body, plus a glossy epidermis looking like it has been varnished. But otherwise there is not a lot to tell G. denudatum and G. horstii apart, since they both have a similar white flower. As MD says there are a lot of misidentified plants on the Web, therefore you really need to compare them with the original descriptions. Perhaps I was lucky since I was collecting when Horst Uebelmann first introduced these species into cultivation under their HU numbers so can recognise them.

The true G. horstii is not that common in cultivation in the UK anymore, since just like Notocactus uebelmannianus and it's v. flaviflorus, nurserymen only usually propagated the one with the red or pink coloured flower that sold better. I had to get a start again of the genuine glossy body white flowered HU horstii from Graham Charles since all the dealers offered was v. bueneckeri, though many mistakenly simply called it horstii, which has a white not a pink flower.

Gymnocalycium horstii ssp. bueneckeri, an old original plant often just sold as "G. horstii" in the UK, but G. horstii has a shiny body and white flower.
This is G. denudatum with it's spines largely adpressed to the body and varying from straight to curly.

http://www.llifle.com/Encyclopedia/CACT ... _denudatum

I put "G. horstii" into Google images and 98% showed pictures of v. bueneckeri as horstii, that is just how much the species have got confused by sloppy labelling.

This is the true shiny bodied G. horstii. G. denudatum having a dull body like G. horstii v. bueneckeri, but in that case one has white and the other pink flowers. The original HU ones were pure white flowers but some later collections like that below have flowers flushed slightly pink, but not as intense as G. horstii ssp. bueneckeri.

https://www.gymnocalycium.fr/gymnocalycium-horstii/

So, we wont be able to tell v. bueneckeri or denudatum unless it blooms? Because regular horstii has a shiny surface so its immediately out of the picture.

Well, a commoner indeed, but perhaps not so simple. Thank you Aiko for the initial identification. And thank you everyone else for your very insightful and thought provoking input. My Gymnocalycium denudatum was indeed bought at a local greenhouse here in Ontario and it is undoubtedly from a large distributor. It is common, simple and plain. But I love it. Cheers. Andrew
Thanks again!