Mammillarias are called such because the spines are all on the tips of ‘nipples'. In all cacti, the area the spine comes off is called the areola; the name is particularly apt with this genus. Most other cacti have areolas lined up along ribs. The flowers of this genus arise from an area between the areolas, at the junction of two nipples. Most other cacti flowers arise from the areolas.
Mammillaria compressa showing pronounced nipples and flowers between them.
These are relatively small cacti, some with relatively small spines. Some plants are mature at just an 1 inch or so tall, though some larger barrel species can grow over 1 foot in diameter and nearly 2 feet tall. Some sucker and some seem to be solitary. Flowers tend to be relatively small for a cactus species, but some Mammillarias have larger flowers than others.
Mammillaria theresae is only a half-inch tall and wide.
(left) Mammillaria geminispina, a nice large clump about 2 feet wide with typically small flowers. (right) A small Mammillaria grahmii with a relatively large flower.
I find many species of Mammillaria do great with a lot of summer watering, but some cannot tolerate much--if any--winter water. However, most of the plants in this article seem happy as can be with drenching cold rains all winter long (I grow all my cacti outdoors with only minimal shade, in the form of larger surrounding plants.) Many Mammillarias seem to enjoy full, hot summer sun, but some obviously do not; I have few of those left in my collection. Though I used to grow all my cacti in the ground, I have run out of suitable ground space so now I am relearning out to grow cacti in pots (some are easier this way... and some are tricky.)
Mammillarias and other cacti in Huntington Gardens in full sun doing well
Having moved a number of Mammillarias about the yard I find them quite tolerant of disturbance with most only having small roots. Some of the bigger species have much more impressive root systems, and a few even seem to have what I would call an underground caudex. This caudex does NOT tolerate being chopped apart when digging up a plant, so be careful when moving larger species.
You can see from these photos how these relatively large plants grow happily in fairly small pots; their roots are pretty small
Most Mammillarias are from Mexico and many of those are somewhat touchy with cold, but some are not. And some Mammillarias are from the U.S. and seem to tolerate far more cold than we ever get here in southern California. There are over 300 species of Mammillarias and I only claim to have experience with 3 to 4 dozen species.
Two U.S. natives, Mammillaria grahmii (photo by Xenomorf) and Mammillaria longimamma (growing in my garden)
Two Mexican natives, Mammillaria bocasana and Mammillaria carmenae. It is hard to predict which will be hardy by just looking at them. It turns out Mammillaria bocasana is an extremely hardy and easy to grow species while the latter is (for me) nearly impossible to keep alive outdoors
For more information and assistance with identification of Mammillarias go to one of the web sites listed below. From persusing the thousands of photos on these web sites, you will notice many Mammilliarias look a LOT alike while at the same time there is a huge variation of appearances within many of the species. That makes identification of an unknown plant a huge challenge. I would say it's nearly impossible, but many people are able to do it by counting areolar spines, noting their positions, checking minute floral details etc. If I cannot tell by a glance, I find further efforts frustrating, and for that reason many of the Mammillarias I grow are just 'Mammillaria species'. I've learned to appreciate each plant for what it looks like, and not always for what it really is.
The following species are among those I have grown and are still alive in my garden (so they must be hardy!)
Mammillaria backbergia is a pretty hardy species as it growing outdoors in the Huntington garden in full sun. It is a suckering, columnar plant with pink flowers.
(left and middle) Mammillaria backbergiana in the Huntington growing in full sun year round (right) My own Mammillaria backbergiana, though its ID is in doubt
Mammillaria bocasana (aka Snowball or Powderpuff Fishhook Cactus) is a surprisingly hardy species with fuzzy white hairs sneakily hiding the sharp hooked spines that grab you as you touch to pet it. I say surprisingly since cacti with fuzzy soft hairs always look like the sort of delicate plants that would rot effortlessly. But I have two that get loads of water year round and I can't seem to rot either of them. Flowers are pale yellow with pink.
(left) One of my two Mammillaria bocasanas, both doing great. (right) Bizzare form of this species call Mammillaria bocasana 'Fred'
Mammillaria compressa is one of the larger species of Mammillaria, forming large dull, pale green mounds with sparse white spines and pink flowers. I dug up one of these in my yard and it had a massive caudex-like root. It looks like it could survive for years off the water stored in the root, but I haven't the courage to try to find out.
Mammillaria compressa outdoors at the Huntington, and my own potted plant
Mammillaria decipiens var. camptotricha is a low-growing, prominently ‘nippled' species with long, curled with spines that cross each other forming a sort of bird's nest look (and it is appropriately called the Bird's Nest Mammillaria). This plant has done well for me in both pots and in the landscape, but I have managed to rot this one by pouring the sprinkler on it directly over and over in hot weather... so be careful.
(left) My Mammillaria decipiens v. camptotricha in its orginal form. (right) A new cactus grown from a sinlge globe of the original
Mammillaria elongata comes in several different colors and shapes. There is a copper-spined version, a normal-spined version, a brain shaped- monstrose version and a crested version. The latter two are a tad prone to rot and desiccation, while the other two are quite hardy and easy to deal with. Flowers are yellow or pink.
(left) Yellow flowering version. (middle) A copper-spined version wtih pink flowers in my yard. (right) My cristate 'brain cactus'; all these are common forms of Mammillaria elongata
(left) Large colony of Mammillaria elongata outdoors in California. (right) Cristate version of the copper-spined form
Mammillaria formosa subsp. microthele is a super-short-spined globular plant that is both hardy and user-friendly (spines can't hurt you). I have three plants that all survive outdoors year round, but none seem to grow or be really happy. So my guess is these are all on borrowed time and may not be all that hardy after all.
(left and middle) Mammillaria formosa subsp. microthele showing extremely short, harmless spines (right) Show plant.
Mammillaria geminispina is a variable species from what I can tell, with some forms having long spines while other forms have short spines. Some form large clumps of ovoid cacti while others form smaller groups of more columnar plants. Some have pale yellow flowers while others have pink. Of course it is possible that I am must mixing up these variants with other species that just look like them. I have to admit here that many Mammillarias tend to look alike. But hardly any other species can beat these plants for hardiness. I have yet to kill any of them by either under or overwatering them, or putting them in too much hot sun. I haven't tried growing them in shade yet but my guess is they wouldn't do well in that situation.
(left) Long-spined version in large pot. (middle) The more common short-spined version in smaller pot. (right) Plant sold to me a Mammillaria geminispina but has pale yellow flowers.
(left) Cristate version of Mammillaria geminispina in a plant show. (right) Colony of Mammillaria geminispinas in the Huntington
Mammillaria hahniana 'Superba' is almost too good looking to be true. This mounding white fuzzy pile of cactus globes looks more like a bunch of little angora pillows than a member of a spiny genus of plants. But despite its delicate appearance, I have not had any problems with this one, even when planted out in full hot sun and receiving sporadic waterings. Its brilliant pink flowers really set off the pure white hairs that cover up some of the deeper, short spines.
(left) Mammillaria hahniana 'Superba' has survived two hot summers and a winter in full exposure to the elements. (right) The more 'normal' form of this species.
Mammillaria karwinskiana is a dark green mostly solitary (to slowly dividing) plant with pink or bright yellow flowers and short, sparse spines. I may find the bright yellow flowering cacti are something else, but they sure LOOK like this species otherwise. This plant seems quite hardy as I have yet to kill either of mine. Both get variable light from hot sun to shade part of the year, and watering has been erratic, to say the least.
Mammillaria karwinskiana is a very durable species!
Mammillaria longimamma is one of the more popular species; the Dolly Parton of the Mammillaria world with extra large nipples. This species has sparse, thin spines and large (for a Mammillaria) bright yellow flowers.
(left) Mammillaria longimamma outdoors in Huntington Gardens. (right) My own plant, flowering.
Mammillaria matudae (aka the Thumb Cactus) is one of my favorite species reliably flowering yearly and growing steadily despite falling over once it gets too tall. It is a suckering, tall columnar species (my largest would be 2 feet tall had in not fallen on its side a few years ago) with very short, tightly knit spines (allowing easy handling with minimal poking) and a characteristic ‘halo' of brilliant pink, closely spaces flowers near, but not at the top of each column.
Several photos of two of my Mammillaria matudae. The plant on the left is over 2 feet long (tall, had in not fallen)
Older mature show plant of Mammillaria matudae
Mammillaria muehlenpfordtii is the hardest of all the Mammillarias to spell and I have no idea how to pronounce it. And I am not sure I have it, either. Online photos of this species show a remarkable variation from one website to another. Either way, the plants I have that were labeled this are doing well and seem comfortable in my dangerous yard. These are columnar/barrel plants that are usually solitary.
(left and middle) Plants sold to me as Mammillaria muehlenpfordtii. (right) A healthy colony growing outdoors in Pasadena, California.
Mammillaria mystax is a plant I have seen at the Huntington and is obviously quite hardy. It's a larger barrel-shaped solitary plant, though how this plant actually differs from Mammillaria gigantea I have not figured out yet. I have one or the other or both; either way, the plants are fairly hardy and tolerate watering abuse as well as some shade and hot, mid-summer sun. Spines on these two species are relatively thick and short giving an overall very neat and geometric appearance.
(left and middle) Two of my Mammillaria mystax. (right) At Huntington, showing both flowers and seed pods (the red tubes with white tips.)
Mammillaria rhodantha I have two forms of this species with Mammillaria rhodantha var. pringlei being by far the more commonly available of the two. This latter form is available all the time at all the garden outlet nurseries and for good reason: it is solitary, easy to grow, moderately large and has beautiful golden long spines. The other form of Mammillaria rhodantha has red spines but is otherwise fairly similar.
(left) Mammillaria rhodantha var. pringlei. (middle) The 'normal' version of Mammillaria rhodantha. (right) Both forms in pot with other cacti.
Mammillaria supertexta is another user-friendly species with such short, tightly knit spines that they cannot penetrate ones skin. This is a columnar suckering species (though slow to offset) with white very short spines and bright pink flowers. I have rotted one, but the others seem OK so far. I cannot personally tell this from the short-spined version of Mammillaira albilanata... and I may in fact have this species instead of Mammillaria supertexta.
two of my Mammillaria supertextas and third shot is of the long form of Mammillaria albilanata, which these two plants of mine could be, but of the short-spined versions.
Mammillaria theresae is an amazing plant whose hardiness would not be anticipated. And to tell the truth, mine died, but not due to any lack of hardiness. It is such a small species--mature plants that flower may only be 2 inches tall and less than 1 inch thick--with such short white super-thin spines they can hardly qualify as spines at all. It just looks like the sort of thing that would rot without hesitation. But I had it in partial shade and watered in freely as it grew steadily year after year, until its untimely demise. I had it planted in a dinky pot that fell multiple times, thanks to certain wildlife knocking it over. The plant finally got trampled by the dogs. Oh well...
(left and middle) My own Mammilliara theresae, growing from a half-inch tall to nearly 3 inches tall before getting trampled. (right) A mature show plant.
Mammillaria velatula subsp. gracilis var. fragilis (also known as Mammillaria gracilis, or the Thimble Cactus) is the longest name of all my Mammillarias, but a great and hardy potted plant. It's too small and physically fragile for a garden plant, with small globoid, offsetting heads about 1 inch diameter max and white, user-friendly spines flattened against the body of the plant. The only problem with this plant is it's hard to move without it falling apart. The offsets and suckers readily fall the main globe if disturbed.
Two different show plants of Mammillaria vetulina ssp gracilis and my own plant in third photo
Mammillaria voburensis is not one of the more ornamental species with dark maroon- green globes about 3" in diameter that sucker profusely and have a sort of ‘dead' appearance (thanks to the color) all the time. However it is a hardy plant and does well in the landscape as well as in pots.
(left) Mammillaria voburensis in my garden. (right) Potted plant for sale at a nursery.
The following are a number of easy species that I am unable to identify at this time. If anyone recognizes any of these, please let me know!
There are hundreds of other Mammillarias and many are fairly hardy. Below are a few of the hardy ones that I have no experience with, followed by a smattering of other Mammillarias just to give you an idea of the diversity of this genus. Most Mammillarias are cheap, so start collecting today!
Mammillaria gigantea growing in my yard
(left) Mammillaria beneckii (middle) Mammillaria bombycina (right) Mammillaria canelensis
(left) Mammillaira casoi (middle) Mammillaria crinita (right) Mammillaria crucigera
(left) Mammillaria duwei in my yard; sadly it did NOT turn out to be a hardy species. (middle) Mammillaria haageana (right) Mammillaria huitzilopochtlii (photo by CactusJordi)
(left) Mammillaria humboltii (middle) Mammillaria lasiacantha (right) Mammillaria lenta
(left) Mammillaria magnifica (right) Mammillaria magnimama
(left) Mammillaria parkinsonii (Owl Eye Cactus) (right) My own plant. It rotted but probably was hardy; I had it in a shady spot
One of the favorite species among collectors, Mammillaria plumosa, another 'user-friendly' species (easy to handle without getting poked)
(left) Mammillaria pseudocrucigera (middle) Mammillaria schiediana (right) Mammillaria spinosissima, another hardy species.
(left) Mammillaria uncinata (right) A variegated Mammillaria wagneriana