This member of the Euphorbiaceae family was given this name by John Torrey in 1859. It is found in north-western Mexico and south-eastern Arizona in the US, growing in a well drained sandy soil with some water and lots of sun. The caudex can grow to seven centimetres in diameter, the entire plant from fifteen to 150 centimetres in height. The flowers are white.
The name is derived from the Greek words κνίδη (knide), meaning 'nettle' and σκολος (skolos), meaning 'thorn' or 'prickle'. The species name from Latin; angusti; 'with narrow' and Latin; dens; 'tooth'. The fruit by Ken-ichi Ueda, Inaturalist.org. Large plant by Thomas Van Devender, Swbiodiversity.org. The leaf by Thomas Van Devender, Swbiodiversity.org.

