Mammillaria spinosissima ‘Un Pico’ (Bald-Headed Irishman)

Mammillaria spinosissima ‘Un Pico’ after I bought it home at 1 1/2″ tall x 1 5/8″ wide on 4-3-21, #899-8.

Mammillaria spinosissima ‘Un Pico’

Red Headed Irishman, Spiny Pincushion Cactus

Mammillaria spinosissima

mam-mil-AR-ee-uh  spin-oh-SIS-ee-muh

Plants of the World Online by Kew lists 107 synonyms of Mammillaria spinosissima which you can see HERE. I didn’t want to add the whole list on this page…

Mammillaria spinosissima Lem. is the correct and accepted scientific name for this species of Mammillaria. It was named and described as such by Antione Charles Lemaire in Cactearum Aliquot Novarum in 1838.

There were several infraspecific taxa for Mammillaria spinosissima but now they are listed as synonyms of the species… 

The genus, Mammillaria Haw., was named and described as such by Adrian Hardy Haworth in Synopsis Plantarum Succulentarum in 1812.

As of 11-12-21 when this page was last updated, Plants of the World Online lists 154 species in the Mammillaria genus. It is a member of the plant family Cactaceae with 146 genera. Those numbers could change as updates are made on POWO.


Mammillaria spinosissima ‘Un Pico’ on 4-3-21, #788-9.

I brought this cactus home from Wagler’s Greenhouse (one of three Amish-owned local greenhouses) on 4-3-21 labeled Mammillaria spinosissima ‘Un Pico’. Actually, I saw about 40 or so of these plants on Thursday but  I wasn’t sure if I possibly already had one. I knew I didn’t have one by that name, but you know how plant names change, and I have several that looked similar. I wrote down the name to double-check to make sure it wasn’t a synonym of a species I already had. When I found out I didn’t have this one, I went back on April 2 and found out that they had been moved. When I did find them, they were in a different location and there were only a few left. Unfortunately, it was Good Friday so they were closed. One of Mrs. Wagler’s granddaughters hid one I selected and I picked it up the next day.

The species Mammillaria spinosissima is a highly variable and VERY spiny species of cactus. The cultivar ‘Un Pico’, however, is a selection of a stable genetic mutation that only produces one long central spine and some may have none. The particular plant I brought home, however, has a few areoles with more than one spine. Time will tell if it is actually a Mammillaria spinosissima ‘Un Pico’ because it has some growing to do… Common names for the species include Bald-Headed Irishman and Spiny Pincushion Cactus. “Un Pico’ should be called the Bald-Headed Irishman (even though the species is a native of Mexico).

When I brought this plant home, I measured it at 1 1/2” tall x 1 5/8” wide. It was in a 4 1/4” diameter x 3 1/3” tall pot. I will repot this plant and put it in a mixture more suitable for cactus and check its roots for a plug wrapper. I don’t like my plant’s roots having to try and grow through the wrapper…

Mammillaria spinosissima ‘Un Pico’ (Bald-Headed Irishman) at 3″ tall x 1 7/8″ wide on 8-18-21, #827-22.

I measured the plants on the front porch on 8-18-21 instead of wating to do them all as I bring them inside for the winter in October. I didn’t have them inside until October 28 in 2021 because there wasn’t an “F” in the forecast until then. The Mammillaria spinosissima ‘Un Pico’ did very well over the summer and grew to 3″ tall x 1 7/8″ wide. It doubled in height…


Family: Cactaceae
Origin: The species is native to Guerrero and Morelos in Mexico.
Zones: USDA Zones 10a-11(30 to 40° F/-1.1 to 40° C)
Size: Slowly to about 10-12” x 4” diameter.
*Light: Sun to part shade.
**Soil: Fast-draining. Good quality potting soil amended with pumice (50/50) or additional perlite and chicken grit (2-1-1).
***Water: Average during the summer, barely if at all during the winter.

*During the summer, I keep most of my cactus on the back deck where they receive full sun. During the winter most cactus aren’t picky about the light because they are basically dormant. For several winters, mine were in front of the east-facing sliding door in the dining room so they didn’t get much light but they did great. I built a new shelf for the bedroom so now they are in front of a west-facing window. Most of the succulents are on a shelf in a south-facing window in a cool bedroom but a few are in my bedroom.

**When it comes to potting soil, finding the “sweet spot” is not exactly that easy when materials are limited. Cactus and succulent enthusiasts (and experts) do not recommend using peat-based commercial mixes but what choice is there for most of us. They say to use a loam-based mix… Hmmm… Our soil is loam, so do I just use dirt? Well, no because “dirt” is heavy and you need a “light” material. There is A LOT of cactus and succulent recipes online and some get pretty elaborate. Many say to use sand as an ingredient, but if you do that, it needs to be very coarse, like builders sand, because “ordinary” sand, like for sandboxes, is too fine and it clogs up the air space between the coarser ingredients. For MANY years I used 2 parts Miracle Grow or Schultz Potting amended with an additional 1 part of perlite and 1 part chicken grit. Schultz doesn’t seem to have as many large pieces of bark. Cactus and succulent enthusiasts recommended using pumice instead of perlite and grit so I checked it out… The “guy” at General Pumice (online) recommended using a 50/50 mix of potting soil and pumice. General Pumice has 3 different sizes to choose from depending on the size of the pot. SO, in 2018 I bought a bag of 1/8″ and mixed it 50/50 with Miracle Grow Potting Soil. I liked it pretty well. Then in 2020, since most of the cactus were in larger pots, I ordered the 1/4″ size. Pumice has a lot of benefits over perlite and has nutrients that are added to the soil when watering. Pumice is also heavier so it stays mixed in the soil instead of “floating” to the top. Still, there is the issue of the mix getting very hard once you stop watering the plants during the winter when you stop watering. I think this is because of the peat in the potting soil… SO, instead of re-potting the cactus and succulents in the spring, I started doing it during the fall and winter so their soil would be loose. Since you don’t water as frequently during the winter if at all, the timed-release fertilizer does not activate. I have not tried coir, but I am looking into it…

You have to sort of mimic the soil where species grow in their native habitat. For that, you almost have to go see for yourself… Typically, they grow in fairly rocky soil.

***I water my cactus and succulents on a regular basis during the summer but barely ever in the winter (maybe a little in January) until close to time to take them back outside.

You can read my Cactus Talk & Update and Cactus & Succulent Tips to get my opinion about growing cactus and succulents.

When you bring your new plants home from the store, you need to check their roots and the soil to see if they are wet. If so, you may want to re-pot it right away. It is advisable to re-pot them in a better potting soil more suitable for cactus and succulents.

There isn’t much online about the species or ‘Un Pico’ except for online stores. I will continue adding more photos and information as time goes by. 

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. Please click on “like” if you visited this page. It helps us bloggers stay motivated. 🙂 You can check out the links below for further reading. The links take you directly to the genus and species of this plant. If you see I have made an error, please let me know in a comment or email me at


NOTE: The figures may not match on these websites. It depends on when and how they make updates and when their sources make updates (and if they update their sources or even read what they say). Some websites have hundreds and even many thousands of species to keep up with. Accepted scientific names change periodically and it can be hard to keep with as well. In my opinion, Plants of the World Online by Kew is the most reliable and up-to-date plant database and they make updates on a regular basis. I make updates at least once a year and when I write new pages and add new photos but I do get behind. We are all a work in progress. 🙂


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