Agave asperrima 

Agave asperrima used to be called Agave scabra. The name is sometimes used synonymously.

Agave asperrima species, subspecies, varieties and forms

Agave asperrima (Sierra Del Carmen, MX Big Bend Form sold by Ethical Desert) 

Hardy to -11° possibly lower, but may take damage

Agave asperrima ssp. maderensis 'Grand Duke'

Hardy to 10°

Agave asperrima spp. potosiensis, Potosi Agave 

Hardy to 5-10° (the variegated form is only hardy to 15°)

Agave asperrima ssp. zarcensis, Zarca Agace 

Hardy to 15°