Leuchtenbergia principis W. J. Hooker
Growth Habits: Very slow growing, usually solitary,up to 30 inches tall (75 cm), grows a large tap root so will require a deep pot to allow the root some room.
Scientific name: Leuchtenbergia principis
Common names: Agave Cactus, Cob Cactus, Prism Cactus.
Synonym: None found
Etymology: Named in honour of Eugene de Bauharnais, the Duke of Leuchtenberg and prince of Eichstadt
princeps :- meaning a prince
Origin: North-central Mexico (San Luis Potosi, Chihuahua)
Light: Full sun to light shade.
Compost: I grow mine in my usual standard castus mix.
Water: Water carefully in summer, lack of water will make the tip of the tubercles yellow. Too much water will make it rot.
Flower: Large yellow flower when plant reaches the right age (mine was about 5 years old before it flowered)
Min temp: I keep mine at about 5 c (41f) in winter although they will tollerate a small ammount of frost for short periods it is best avoided.
Cultivation: Lower "leaves" will shrivel and fall off as it grows older, it is not advisable to bury the resultant part of the stem.
References. http://cactiguide.com
http://www.desert-tropicals.com
http://www.cactus-art.biz
Comments. A monotypic genus that has not been interfered with over the years, thought to be closely related to Ferocactus, it has been crossed with a Ferocactus to create a hybrid called a Ferobergia.
I bought my plant as a young seedling in 2007 and this year (2011) was its first year flowering.
Flower close-up
Young seedling
Mature plant photographed at the BCCS National show in 2008