cas·car·a buckthorn 
(kă-skărə)
(kă-skărə)n.
A buckthorn (Rhamnus purshiana syn. Frangula purshiana) native to western North America, the bark of which is the source of cascara sagrada.
[Spanish cáscara, bark, from cascar, to break off, from Vulgar Latin *quassicāre, from Latin quassāre, frequentative of quatere, to shake; see kwēt- in the Appendix of Indo-European roots.]