Friedrich, H.; Glaetzle, W. (1 December 1983). "Seed-morphology as an aid to classifying the genus Echinopsis Zucc". Bradleya. 1: 91–104. doi:10.25223/brad.n1.1983.a9. S2CID90895449.
Friedrich, H.; Glaetzle, W. (1 December 1983). "Seed-morphology as an aid to classifying the genus Echinopsis Zucc". Bradleya. 1: 91–104. doi:10.25223/brad.n1.1983.a9. S2CID90895449.