Echinopsis, which is placed in the Cactaceae family, is a large genus of 128 species of cacti which grow naturally in the South American countries of Argentina, Chile, Bolivia, Peru, Brazil, Ecuador, Paraguay and Uruguay. They grow in sandy or gravel soils on hillsides and in rocky crevices. They range in size from large tree-like species, to small species such as Echinopsis chamaecereus, the peanut cactus. They have large, showy flowers which seldom last longer than a day; however they are such prolific bloomers that they can be covered with flowers for days on end. Echinopsis is distinguished from other genera by the length of the flower tube, the form and size of their stems, and from where the flowers occur on the stem. Some common names include hedgehog cactus, sea-urchin cactus and Easter lily cactus. Due to the large number or species, and large number of variations, it has made classification of species in this genus very difficult. This has resulted in a large number of synonyms for Echinopsis, most of which used to be considered separate genera, but are now included in the genus Echinopsis. All these synonyms are still widely used by collectors and enthusiasts and there is much debate and controversy as to the correct classification. The name comes from the Greek word echinos meaning ‘spiny’, ‘hedgehog’ or ‘sea urchin’, and opsis meaning ‘likeness’ or looks like. Echinopsis can be grown as pot plants and make interesting features on a sunny veranda. They also make an attractive addition to a rockery or water-wise garden.

Echinopsis macrogona, syn. Trichocereus macrogonus or Cereus macrogonus is a species of cactus native to Bolivia. It is closely related to Echinopsis pachanoi (syn. Trichocereus pachanoi), the San Pedro cactus, and Echinopsis peruviana (syn. Trichocereus peruvianus) the Peruvian Torch cactus. This specie has ethnobotanical uses and also contains the psychoactive alkaloid mescaline. It has a shrubby growth habit, and the stems are characterized by its bluish-green skin, with a diameter of up to 9 cm, and height of between 2 to 3 m. There are between 6 to 9 prominent ribs with grey coloured areoles where 1 to 3 central spines up to 5 cm in length and yellow to brown in colour, are surrounded by 6 to 9 shorter radial spines up to 2 cm in length. The large, white flowers are borne at the top of the stems and can be up to 18 cm in diameter.