Leuchtenbergia principis, also known as The Agave Cactus. This one is very fussy when it comes to drainage. I pot them in a pot with a large drainage hole, a few crocks in the bottom and a very gritty well drained mix. I also prop the pot up after watering to let it drain properly. It's not that they don't like watering, they enjoy a good soak, they just don't want their roots staying wet. I've not grown them from seed yet (The seed I bought online turned out to be Echinocactus grusonii 🙄) The smaller plants I have bought have both had shrivelled tips, probaably as the plants didn't like the watering they got. After repotting and sticking to a watering regime they have recovered well and are showing good new growth.  They like a lot of light but benefit from a little shade from the midday sun. I feed once a month in the summer with dilute tomato feed.

They do develop a large turnip like root so will need potting on into bigger pots as they grow. Keeping in mind the need for good drainage, it would be wise to check if the pots need extra drainage holes before potting on. It's easy enough to drill extra holes in terracotta before planting, not so easy afterwards.  They will reach 700mm/28 inches so will get to be quite an impressive plant.

I've tried taking tubercle cuttings in the same way as I have done with Mammillaria longimamma but without success. I used the smaller tubercles from the bottom of the plant, it may well work by using the larger, fleshy tubercles from higher up the plant but it seemed a shame to disfigure the plant.  The larger of the two plants I have flowered last year, so now that I have two plants I'm hoping they will both flower this year so I can cross pollinate them to get viable seed. 

They are found in Mexico in semi desert on calcereous soil, 1,500 to 2,000 Metres above sea level. Population estimate is more than 500,000 but considered to be threatened by illegal collection and grazing. 

This is a monotypic species but is closely related to the Ferocacti, which it will cross with.  It's also apparently been crossed with Thelocactus, Stenocactus and Coryphantha. There is a monstrose and a cristate type as well. 

While I can't see me growing enough of these plants to maturity in order to put them up for sale in our shop (They're quite slow growing and I'm no spring chicken) I will carry on buying the odd small plant to grow on, giving cuttings another go and hopefully produce some viable seed this year. It's a lovely plant to grow, has lovely flowers and incredible long papery spines that are a very good addition to our cactus house.