I have a cactus that has been identified as a mammillaria marksiana, but it has arms growing from the top. I have not seen any photos that are growing like mine. Mine does not have any "babies" growing around the bottom as seen in photos. Has my cactus been misidentified? In all other respects, it does look like a mammillaria marksiana.

It is a Mammillaria but marksiana doesn't seem right. What its doing is a very common Mammillaria characteristic - its branchng dichotomously. Some species are better at it then others and its always fun when it happens.

Your cactus is beautiful, you are doing a good job with it. Has it bloomed? Flowers would help determine which Mammillaria you have.

I agree with @Daisyl, marksiana does not seem right. I would explore Mammillaria karwinskiana subspecies nejapensis which does occasionally pup basally but more commonly increases dichotomously.

I would like to amend my previous possible ID. While I have always known this plant as Mammilaria nejapensis and there are hundreds of pictures of this plant online labeled as M. nejapensis or M. karwinskiana subsp nejapensis, I researched the original description and it clearly states "no central spine". I still believe that it is a form of M. karwinskiana but it is not nejapensis. The good news is that the care listed for all these misidentified plants is correct no matter what it is called.
I have discovered, as I've aged, that just because you bought a plant from a reputable nursery and committed the name and look to memory you can be wrong. I've passed on incorrect info many times. Now if I could learn to just slow down and research before I answer....

Yes, it has bloomed several times with a ring of small straw like yellow flowers. That is why I assume it to be a marksiana. I do worry about it's shallow root systems. I need to keep rotating it away from the sun, and prop the leaning side with rocks and a stick.

I too believe its Mammilaria nejapensis. Wildbloomers didn't list her references where it states we are all wrong so I think I'll stick with M. nejapensis (sorry Wildbloomers). I just took a couple photos of mine and guess what, a dichotomous split is about to happen. I love it when that happens.

How do you know about the split?

Notice how the center of the cacus (in photo #2) is an oval instead of being round. That's the first sign.

My cactus was a gift from my daughter about 7 years ago, who may have gotten it from a Walmart. It was about 2-3" and had fake flowers glued to it.
I managed to remove them without damaging the plant. Thank you for all the responses. It was never vital for me to know exactly what it is, but I wondered why I could not find a photo of one that looked quite like mine.

@Daisyl. We agree on what plant we're talking about, just not it's name. I have called the pictured plants M. nejapensis for years. The Catalog of Life that the NGA uses as its definitive source for valid scientific names does not recognize M. nejapensis. The correct name is M. karwinskiana subsp nejapensis. Even this sites own plant database lists that plant as M. karwinskiana with three subspecies, karwinskiana, nejapensis, and beisellii. Of these, only subsp beiselii has a central spine, sometimes long, sometimes short. My point is that sometime long ago someone misidentified a plant, mass-produced it and we all bought in. It happens. Aside from online sources (world Plants, LLifLe etc) I have books by Britton and Rose, Anderson, Innes, etc. They have one thing in common, that name is invalid. FYI my plants are still labeled M. nejapensis, wish I knew what it really is.

I do not understand the confusion. The plant in question does not have a central spine it has a very much longer lower radial spine compared to its other radial spines - exactly as M. karwinskiana ssp. nejapensis is described.

No, I'm not understanding either. The plant is Mammillaria karwinskiana ssp. nejapensis and it is listed in Catalog of Life as an accepted name. As mcvansoest pointed out, the description is also correct.

https://www.catalogueoflife.or...

Upon enlarging it on my computer instead of my phone I see that that in the original posted picture I mistook the longer lower radial to be a central, my mistake. On your picture Daisy, the central spine is unmistakeable.

Yep, you are correct there. On paper that would make it a 'regular' M. karwinskiana which may or may not have a central spine.

Given that the ranges of both overlap I am not surprised things made it to market as seeds from a, but turning out to be b, which occurs nearby or in the same area...

So mine is not nejapensis? Its a hand written (by me) label so probably came from a local store not from someone who actualky knows something.

Daisy, I found an old post on Dave's Garden that may help you ID your plant if you're into counting spines etc.

On Mar 17, 2005, Xenomorf from Phoenix, AZ (Zone 9b) wrote:

The differences between the subspecies are:
--ssp. karwinskiana; has medium yellow flowers with purpleish midviens; No central spines and 6 radial spines.
--ssp. collinsii; has white flowers with deeper pinkish midveins; One central spine and 7 radial spines.
--ssp. beiselii; has white flowers with red tinted midveins; One central spine and 5-8 radial spines.
--ssp. nejapensis; also has white flowers with red tinted midveins, but the spines are larger and white and has much more wool; No central spines and 3-5 radial spines per areole.

Note that subsp collinsii is recognized in the COL as M. voburnensis subsp collinsii (Britton and Rose) U. Guzman and that even the experts can get it wrong as shown below. Look how many times Britton and Rose had their original description and name changed as new info came about.
Mammillaria karwinskiana subs. collinsii (Britton & Rose) D.R.Hunt
Mammillaria collinsii (Britton & Rose) Orcutt
Mammillaria voburnensis subs. collinsii (Britton & Rose) U.Guzmán
Mammillaria voburnensis var. collinsii (Britton & Rose) Repp.
Neomammillaria collinsii Britton & Rose

One last comment, your plant is beautiful and well grown!

Thank you but that sounds like way too much work. If I do, I'm afraid I'm going to have to find something more credible than something written by someone named Xenomorf on Dave's Garden. Is this guy an expert? Credentials?

Of course, I wouldn't take anything I say on this Forum as the absolute end all answer either.

No, it looks like he/she just consolidated the info from LLifLe I copied it because it was easier than doing the cut and paste myself.

The thing is that in those consolidations quite some info gets lost. The books I have all suggest that M. karwinskiana ssp. karwinskiana can have 0-1 central spines and 5-7 radials ie. it can have a central spine and have 5 radiatls, which would make Daisy's plant M. karwinskiana ssp. karwinskiana given that this is a well known species that has been in cultivation quite long with a range that overlaps that of ssp. nejapensis also a relatively well known 'older' to cultivation plant one of those two as the main candidate is more likely than the two other ssp. which are in one case much newer and and in the older quite a bit rarer, with a distinctly different appearance. The books also suggest that ssp. nejapensis does not have a central spine, but how many specimens from what part of the range will they have looked at?

Anyway, Daisy I suspect your plant may be straight up M. karwinskiana ssp. karwinskiana iso ssp. nejapensis, as it would not be inconceivable for seeds from one to be conflated with the other. In addition labeling it nejapensis might have made the plant more desirable at one point given how karwinskiana is a more common plant with a wider distribution range. On top of that both plants are described as relatively variable so confusion between them may be unsurprising.

As to flower color... I have observed distinct changes in flower appearance from the same plant especially color wise depending on the time of year and the level of heat and humidity, so while helpful in distinction it is not definitive.

My major problem with the Xenomorph/Dave's Garden info is its from 2005. That is like a million years ago in cactus identification, re-classification land.

But I don't really care which karwinskiana it is as I don't plan to add it to the DataBase. I just like its looks: big spines, little thready spines, fur and now dichotomy. Yay!

Fully agree with that they are awesome plants. I have three, which I think are all ssp. nejapensis, but I have not really checked for the presence of a central spine, mine also all came labeled as nejapensis. One has split once so is two headed, another has split twice and the second time in both heads so is four headed and then I have my three headed monster... which split twice but on the second split only in one of the two existing heads giving it a three headed look.