Below is a tricky one to identify.
First we have what is unquestionably Parodia rutilans:
Here’s a picture of the cactus under that giant yellow flower:
Every source I have indicates that P. rutilans and all of its subspecies all have brown spines. Now they can have a more purplish flower too. But the edges are purple, while the center still remains at least yellowish.
Then there’s this plant:
The cactus is superficially similar to the one above. But this one has very clear black spines that fade to gray. You can really see that in the picture. Other aspects of the spination are also very clear and clearly not Parodia rutilans or related subspecies. And while P. rutilans can have a purplish flower, it still has a yellow throat while this one has a whitish throat (the photo shows some reflection of the yellow stamens on the petals).
Also, this flower has had a lot of trouble opening without heat. It’s a spring bloomer and we usually do not have enough heat this time of year for this flower to fully open. So I have lots of pictures from the last few years of this plant with buds, but this is my first one with a fully open flower. Previously, from the spination and the buds I thought this might be an Echinocereus, and with the heat issue that makes a lot of sense too. But now that this flower is finally open I can say very clearly that this is not an Echinocereus.
What is the one factor that makes me certain? The purple stigma.
So what is it?
I have a book that very clearly indicates that this is Notocactus roseiflorus. Case Closed? No! All Notocactuses have been moved into Parodia for a couple decades now, so then the question is what Parodia would this species name have been moved to. And unfortunately the answer is Parodia rutilans. Which clearly this is not. No way. Not even close. Not a subspecies. So I went back and did some more research on Parodia rutilans and the plant at the top and really, it’s quite certain. To quote my copy of Anderson, “Aureoles densely white wooly… Central spines light reddish brown, straight or pointed slightly downward…”
Now I had been using a made up name, Parodia rutilans ssp. roseiflorus to indicate the P. rutilans that had the purplish flowers as mentioned above, but that’s not a real name. I just made it up. So that’s gone by the wayside. So now I have to live with the fact that Parodia rutilans’ flowers can vary and rename all the ones with the brown spines to just simply Parodia rutilans.
And since I can’t come up with any other name ever attached to this black-spined purple-flowered cactus I will have to suffice with Notocactus roseiflorus for now. Unless someone can help me come up with another name that is current.