Mammillaria Vetula sub species gracilis is commonly known just as Mammillaria gracilis. It's well known for producing myriads of offsets or pups, each one of which easily detatches from the mother plant and will very easily root.  It is often dismissed by cactus growers as being of little interest.

If left to it's own devices it will soon be overwhelmed with masses of offsets and end up resembling a sort of cactus frogspawn.

Fig 1 : These offsets have been left untouched since the tray was planted up

However, with regular removal of the offsets the plants will develop into a much more sturdy barrel shape, either with a single head about an inch and a half across or, with selective removal of pups, a multi branched plant with a rather pleasing form. 

Fig 3 : Four year old plant with multiple heads

If you're aiming for a single headed plant then it's quite easy just to rub or twist the offsets off. This needs to be done three to five times a year to encourage the plant to form a single head. Offset production will slow down as the plant ages but will still need doing a few times a year.  If you don't get around to doing it and the offsets get a bit large they tend to leave gaps in the plant but don't worry, they will soon grow out. 

If you're aiming for a multi branched plant then you'll need to select some of the offsets to become the branches.  The ones you leave on will soon start to grow, but until they've matured they will be quite fragile. (One of the older names for it was "fragilis")  It's a bit dishartening to prune a plant for months only to have a branch drop off as you're doing it so when you first chose offsets to save, try to  select ones growing as close to the base as possible. These will be partially supported by the substrate and will have a much better chance of staying on the mother plant to maturity.

If you do accidentally knock a branch off, don't despair, these will easily root up and will make new plants quicker than using the small offsets.

Fig 5 : Rooted Offset.

 I usually have several trays and pots at different stages to keep the shop stocked with both smaller and mature plants.  It's not advisable to save all the offsets, as tempting as this might be, a s you will end up with thousands of plants and will need an extra greenhouse.  The pictures below show various stages of "pruning" the offsets.

Fig 6 : Plant ready for pruning.

Fig 7 : Nearly done. You can see what I mean about not keeping the offsets

The tray below was sown with offsets a few years ago. I take off the offsets a few times a year and don't feed the tray, so the plants slowly mature until needed. They can then be potted up into 3 inch pots and grown on.  If I do need some extra plants it's easy enough to take a few out to let the remaining ones grow bigger.

     So although most people don't give this cactus much thought, it can develop into a nice little plant.  I have even won first prize at Dorset's Melplash Show  in 2017 with one, and there was some stiff competition there.   

      They are one of the first cacti of the year to flower and although the flowers are small they are a welcome sight early in the year. They often have a few more flowers later in the year which are followed by attractive red seed pods which stay on the plants till spring.  Strangely enough, the mice and slugs don't seem to take these pods like they do other Mammillarias.    They can be a bit of a haven for Mealybugs, with lots of places for them to hide. Keep a close eye on them and spray if needed.  I lost a few plants last year when I didn't notice an infestation until they started to collapse. I use Bug Clear twice a year and will give everything a dose of Neem Oil after the second watering.

     It's often puzzled me why a plant that produces so many offsets would expend energy on seed production as well, maybe it just wants to take over the world.