Mammillaria rhodantha Link & Otto is the correct and accepted scientific name of this plant. It was first described by Johann Heinrich Friedrich Link AND Christoph Friedrich Otto in Icones Plantarum Selectarum in 1828.
When I first bought this plant from Wal-Mart on February 1, 2016, the label just said Mammillaria species. I looked a lot of photos on the CactusGuide and Llifle (Encyclopedia of Life) and could not figure it out. Finally, I sent an email and photos to Daiv Freeman of the CactusGuide and he suggested it was a Mammillaria rhodantha. Even though the red spines would be a sure distinguishing feature, apparently I hadn’t looked at enough photos to get that far.
I have noticed that there are other red-spined cactus species since then that look similar but there is always something that separates it from being my cactus. Not that I doubt Daiv Freeman in any way. Popularity and availability would also help determine the name of an unknown variety you obtain. You also have to realize that many species are very variable and have subspecies, forms, and varieties. Apparently, not all Mammillaria rhodantha have red spines. No point in saying you have very rare cactus because of one feature. There are many things to consider so it is best you consult with an expert. That way your options are greatly reduced and you will have peace of mind. 🙂 I always try to buy only labeled plants but sometimes I can’t help myself.
One day in September I noticed it had a bud… It must have already been there for quite a while.
Zones: USDA Zones 9a-11 (20 to 40° F).
Size: 6-12” tall.
Light: Sun to part shade.
Soil: Fast-draining. Potting soil amended with grit and pumice or perlite.
Water: Average during the growing period, barely if any during the winter.
Flowers: Pinkish flowers about any time of the year.
When cooler weather was coming I had to get ready to move the potted plants in the basement. I cleaned off all the pots and removed any old debris out of the pot. You need to give your plants a good look before you bring them inside to make sure no bugs are coming in with them. Sometimes as cooler temps approach some insects may try to hibernate under leaves that have accumulated in the pot or around the base of the plant. I also measure my cactus and succulents periodically because some cactus grows so slow I like to measure them from time to time. On October 17, I moved the plants into the basement and the Mammillaria rhodantha measured 3 3/4″ tall x 3″ wide. I moved most of the cactus and succulents upstairs for winter. I am writing this page on February 21, 2018, and this plant has grown almost 1/2″ more in the kitchen windowsill.
The Mammillaria rhodantha has a few very small buds. Now, let’s see how long it takes for the flowers to open…
I will honestly tell you, the red color of the spines is awesome especially in the sunlight.
Mammillaria species are some of the easiest of all cacti to grow. They need fast-draining soil such as a good cactus mix. I have been using 2 parts potting soil mixed with 1 part (chicken) grit and 1 part perlite. Many cactus people are recommending pumice instead of perlite and some say absolutely no vermiculite. There are several recipes online but some have more ingredients.
You can visit my Cactus & Succulent Tips page for more information.
Once warmer temperatures arrived I moved all the potted plants back outside for the summer.
I put most of the cactus on the back porch and a few on the front porch. The Mammillaria rhodantha is beginning to grow a few buds.
By August 26 the buds were getting larger.
I had to move the potted plants inside for the winter on October 10 because the forecast was calling for an “F” in a few days and the nighttime temperatures were getting cooler. I usually measure the cactus and succulents when I bring them inside and the Mammillaria rhodantha was 4″ tall x 2 7/16″ wide. Last year I messed up and included the spines in the measurement but this year I remembered not to.
November 29 was a nice spring-like day, so I took the cactus to the back porch for a photo shoot. I was working on a post to show the difference between the cactus in my collection.
It takes a LONG time for the buds to open on this plant… Buds form in the axils between the tubercles from the previous year’s growth. There is also a little wool in the axils between the tubercles which disappears with age. Supposedly, maybe on some species, flowering doesn’t occur until after growth of trichomes becomes inactive. Here you see buds forming among the wool between some of the tubercles…
This Mammillaria rhodantha has 4-9 long, reddish-brown, recurving central spines. Other variations do not have reddish-brown spines. It produces 16-24 white (sometimes yellowish) radial spines.
The radial spines on the lower plant can turn somewhat gray looking with age, which Llifle says appear to be dying.
Mammillaria rhodantha divides dichotomously and also produces offsets. Hmmm… I didn’t realize I had so many Mammillaria species that divide dichotomously…
I took a photo of the top part of this cactus because it is very interesting. Many species have a wooly apex but the Mammillaria rhodantha is especially colorful. The wool on its areoles pretty much disappears as the plant ages.
When I measured the cactus on October 10, this plant was 4″ tall x 2 7/16″ wide. Since the Mammillaria pringlei was taller after only a month, I decided to re-measure this one, too. HOLY CRAP! It is now 4 1/2″ tall! Something is definitely weird!
I will continue adding more photos and information as time goes by. The links below take you directly to information about the species, or genus, for further reading.
I hope you enjoyed this page and maybe found it useful. If you have any comments, questions or suggestions, I would like to hear from you. If you find an error, please let me know. I am not an expert. Please click on “like” if you visited this page. It helps us bloggers stay motivated. 🙂