Coryphantha Engelmann 1856
Spread throughout Mexico and North America, Coryphantha generally regarded as poorly understood taxonomically.  Described by Engelmann (1856), Coryphantha was originally considered to be a subgroup of Mammillaria.  The name Coryphantha is derived from the Greek koryphe, for head and anthos for flower in reference to the large blooms sitting at the top of the plant.




Coryphantha cacti are commonly found in the average collector's garden and C. elephantidens is perhaps one of the more well known of the Coryphantha. 

Possessing very large tubercles, plants are commonly referred to as the 'Elephant's Tooth' cactus.  Spines are large and awl-shaped curving out from the tips of the tubercles.

Coryphantha have large showy flowers that are pale brownish to yellow giving way to very large fruit.  The fruit of C. elephantidens is ovoid shaped and fleshy to mucilaginous with ovoid-shaped seeds that are a deep shade of brown.  The fruit of C. elephantidens tends to smell sweet but is tart and not edible.

An excellent source for information is cacti-art.biz, which is a site specializing in cactus plants.
Synonyms:

Lepidocoryphantha Backeberg 1938,

Cumarinia
Buxbaum 1951