Variations 
var. coahuilensis
This is a spineless conical plant has five straight broad ribs and is densely covered with whitish dot-like scales. The diurnal flowers appear towards the top of the plant during mid summer and sulphur yellow coloured with a reddish blotch in the throat.  

It prefers an open sunny position, and grows on very well drained moderately fertile soils.
  
var. columnare
This elongated columnar spineless plant grows to 250 mm (9¾ in) tall by 80 mm diameter with seven to eight prominent ribs that are furrowed at the base and is covered in fine white scales. 

The diurnal yellow funnel-shape flower it is up to 60 mm (2⅜ in) long and wide with a red blotch in the throat. It prefers an open sunny position, and grows on very well drained, stony soils.

var.  potosinum 
This spineless cactus is similar to the species with a dark grey green body with a few whitish scales and has 5-7 straight acute or rounded ribs. The diurnal golden yellow funnel shape flowers are up to 50 mm (2 in) wide appearing throughout summer and the plant prefers an open position with some shade during the hot part of the day.

var. quadricostatum
This spineless cactus has a greyish green body with four even broad ribs that have distinct furrows between them.  It produces bright yellow flowers similar of the species.