The plants growers call Trichocereus, San Pedro among them, are columnar cacti (tall, upright, column-shaped cacti) from the Andes of South America. Each common species has its own entry below, grouped by the country it comes from, with the name Kew uses for it and the Trichocereus name it is sold under.
The short version
- Trichocereus is the name growers use for this group. Kew's Plants of the World Online, the plant-name list kept by the Royal Botanic Gardens, Kew, files most of the species under Echinopsis and some under Leucostele. The second word of the name, the species, often stays the same under all 3 genus names.
- The group grows along the Andes from Ecuador to northeastern Patagonia, from sea level to about 14,800 feet (4,500 m), mostly in dry valleys, on plains and on rocky slopes among spiny shrubs.
- Much of that country is dry for part of the year. In the cardón's valleys in northwestern Argentina, more than 90% of the rain falls from December to March, the southern summer.
- San Pedro is native to southern Ecuador and Peru. Its exact wild origin is uncertain, most likely the Andean valleys of Peru. Peruvian torch and T. cuzcoensis also come from Peru, and Bolivian torch from Bolivia. The tree-sized Argentine saguaro and cardón grow in northwestern Argentina and Bolivia, and most torch hybrids (garden crosses sold as torch cacti) have Argentine parents.
- The same plant can grow more spines in strong sun than in shade, so spines alone are an unreliable guide to which species you have.
- Where a species grows wild is not a reliable guide to how much cold it takes in your garden. Start protecting at 28 to 30 F, earlier for pots and in wet winters, by covering the plant on cold nights. Winter care gives the methods.
One group, three genus names
A botanical name has 2 parts: the genus (a group of related species), then the species, as in Trichocereus pachanoi. Kew's list treats Trichocereus as a synonym, an older name it files under another genus, in this case Echinopsis. It places San Pedro, Peruvian torch, Bolivian torch and most other familiar species in Echinopsis, and the Argentine saguaro, the cardón and T. chiloensis in Leucostele, a genus of 13 species from Bolivia to southern South America. Other classifications keep Trichocereus as a genus of its own.
If your label says Echinopsis or Leucostele, find the species word in the entries below. Trichocereus and Echinopsis names explains why labels differ, and the botanical history of Trichocereus traces how the names came about.
The Andes they come from
In Argentina the group's range reaches the Atlantic coast. It grows from sea level, where T. candicans and T. bolligerianus live, up to about 14,800 feet (4,500 m), where the cardón's species and T. tarijensis reach.
Most species grow on plains of soil laid down by rivers, or on gentle slopes where the soil is shallow, either among grasses or on rocky ground between spiny shrubs.
San Pedro's home is seasonally dry tropical country, and most of the other species grow in desert or dry shrubland. Rain at Cachi, near the cardón's valleys in Salta, northwestern Argentina, averages about 5.7 inches (146 mm) a year, more than 90% of it from December to March. Days and nights there differ by more than 36 F all year.
Peru and Ecuador: San Pedro, Peruvian torch and T. cuzcoensis
San Pedro. Echinopsis pachanoi in Kew's list; sold as Trichocereus pachanoi. Native to southern Ecuador and Peru, and introduced in Bolivia, central Chile, Colombia, Spain and the Canary Islands. In Colombia it is naturalized, meaning it grows wild after escaping cultivation, at about 6,200 to 6,600 feet (1,900 to 2,000 m). Its exact wild origin is uncertain. San Pedro and Peruvian torch are similar enough that one classification treats them as 2 varieties of a single species, and that species most likely grew wild in the Andean valleys of Peru, at about 6,600 to 9,800 feet (2,000 to 3,000 m). Mature San Pedro grows to about 7 to 20 feet tall. Its stems are slender, about 2.5 to 4 inches across, usually with 6 to 9 ribs. Areoles are the small felted pads that spines grow from; on the older ones, San Pedro often has no spines or only 3 to 7.
Peruvian torch. Echinopsis macrogona in Kew's list; sold as Trichocereus peruvianus. Native to western and southern Peru and into Bolivia. In Peru, plants listed as E. peruviana are recorded from 6 departments (Peru's main regions), at about 9,800 to 11,500 feet (3,000 to 3,500 m). Its stems are thicker than San Pedro's, about 6 to 8 inches across. Each older areole has 18 to 20 spines, with 3 or 4 standing out as the biggest.
T. cuzcoensis. Echinopsis cuzcoensis in Kew's list. A species of the Cusco region of Peru, at about 10,200 to 11,800 feet (3,100 to 3,600 m), with upright branches on a tree-like plant up to about 20 feet tall.
Bolivia: Bolivian torch and T. tarijensis
Bolivian torch. Echinopsis lageniformis in Kew's list; sold as Trichocereus bridgesii. Native to Bolivia only. It is one of the tree-like species, growing taller than about 5 feet (1.5 m), found on rocky slopes and in dry valleys. Growers usually place it in Andean valleys at about 3,300 to 9,800 feet (1,000 to 3,000 m). Kew's list includes T. scopulicola in the same species; growers know scopulicola as a nearly spineless form, and why people collect Trichocereus covers forms like it.
T. tarijensis. Echinopsis tarijensis in Kew's list. A tree-like species of Bolivia and the far north of Argentina (Jujuy), and one of the 2 that reach about 14,800 feet (4,500 m).
Argentina and Chile: the giants and the small species
Argentine saguaro. Leucostele terscheckii in Kew's list; sold as Trichocereus terscheckii. Native from Bolivia to northwestern Argentina, at about 2,600 to 4,600 feet (800 to 1,400 m). It grows as a tree 20 to 50 feet tall, with a clear trunk that divides into several upright branches.
Cardón. Leucostele atacamensis subsp. pasacana in Kew's list, a subspecies (a distinct regional form) of L. atacamensis; sold as Trichocereus pasacana. Native to southern Bolivia and northwestern Argentina; its species also grows in northern Chile. That species, T. atacamensis, is the tallest in the group, at up to about 50 feet. In Los Cardones National Park in Salta, at about 8,500 to 10,200 feet (2,600 to 3,100 m), the tallest plants were about 23 feet in the lower zones and about 14 feet in the highest. Young plants are common there, but few reach larger sizes, probably because of drought and frequent frosts, which are harsher higher up. The cardón grows slowly.
T. chiloensis. Leucostele chiloensis in Kew's list. A shrub or tree of northern and central Chile, in subtropical rather than desert country.
T. candicans. Echinopsis candicans in Kew's list. A low species of northern Argentina, from sea level up, spread from La Rioja, San Juan and Mendoza to southwestern Buenos Aires province. Its stems grow upward at an angle, staying under about 3 feet tall, in the shade of thorny trees.
Torch cacti. The torch hybrids are garden crosses, and most of their parent species are native to Argentina. The hybrids form clumps about 2 feet high that lean and spread over the ground.
How habitat shows in the plant
Spines change with light. Light affects how many spines a plant grows and how big they are. On a single branch of a cultivated plant, one areole may have no spines and another up to 10, and wild plants carry many more spines than cultivated ones. If your plant is spinier or smoother than its entry, think about where it has grown: shade or indoors, or strong sun. A plant moved into more sun tends to grow more spines on its new growth, and growers report longer ones too. Move a plant into stronger sun gradually; sun acclimation gives the steps.
Seedlings start beside shrubs. In the cardón's valleys, 96% of the cacti grew right against another plant, most often a creosote bush (Larrea divaricata), and every young plant under about 6 inches tall stood next to another plant. The shrubs may act as nurse plants, sheltering seedlings while they are small.
Pots keep plants smaller. Growers generally find that a plant kept in a pot stays shorter and slimmer than it would in the ground, where it tends to thicken and branch. The life of a cactus covers how growth and height change with age.
Cold. The elevation a species comes from does not tell you its hardiness: a species from 11,000 feet is not, for that reason, hardier in your garden. Winter care covers frost protection, and cactus growing conditions shows how to match the rest of your care to your own climate. Each plant's own figures are on its product page, for example San Pedro, Peruvian torch and Bolivian torch.
Our Trichocereus are grown and sold strictly as ornamental specimens.
Sources
Identity and neotypification of Cereus macrogonus, the type species of the genus Trichocereus (Cactaceae). Sofía Albesiano and Roberto Kiesling, Haseltonia 17: 24-34, 2012. https://cactusconservation.org/wp-content/uploads/2020/03/Albesiano_Kiesling_2012_Haseltonia_17_24-34.pdf
Taxonomía y filogenia de Trichocereus (Berg.) Riccob. (Trichocereeae-Cactaceae). Adriana Sofía Albesiano Hoyos, doctoral thesis, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, 2015. http://sedici.unlp.edu.ar/handle/10915/49922
Trichocereus (A.Berger) Riccob. Plants of the World Online, Royal Botanic Gardens, Kew. https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:289363-2
Leucostele Backeb. Plants of the World Online, Royal Botanic Gardens, Kew. https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:297430-2
Echinopsis pachanoi (Britton & Rose) H.Friedrich & G.D.Rowley. Plants of the World Online, Royal Botanic Gardens, Kew. https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:88444-2
Echinopsis macrogona (Salm-Dyck) H.Friedrich & G.D.Rowley. Plants of the World Online, Royal Botanic Gardens, Kew. https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:132717-1
Echinopsis cuzcoensis (Britton & Rose) H.Friedrich & G.D.Rowley. Plants of the World Online, Royal Botanic Gardens, Kew. https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:88373-2
Echinopsis lageniformis (C.F.Först.) H.Friedrich & G.D.Rowley. Plants of the World Online, Royal Botanic Gardens, Kew. https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:132706-1
Echinopsis tarijensis (Vaupel) H.Friedrich & G.D.Rowley. Plants of the World Online, Royal Botanic Gardens, Kew. https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:88520-2
Leucostele terscheckii (Pfeiff.) Schlumpb. Plants of the World Online, Royal Botanic Gardens, Kew. https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:77122515-1
Leucostele atacamensis (Phil.) Schlumpb. Plants of the World Online, Royal Botanic Gardens, Kew. https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:77122510-1
Leucostele atacamensis subsp. pasacana (F.A.C.Weber ex Rümpler) Schlumpb. Plants of the World Online, Royal Botanic Gardens, Kew. https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:77222592-1
Leucostele chiloensis (Colla) Schlumpb. Plants of the World Online, Royal Botanic Gardens, Kew. https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:77122512-1
Echinopsis candicans (Gillies ex Salm-Dyck) F.A.C.Weber ex D.R.Hunt. Plants of the World Online, Royal Botanic Gardens, Kew. https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:944007-1
Echinopsis pachanoi (Britton & Rose) H.Friedrich & G.D.Rowley. Colombian Plants made accessible (Colplanta), Royal Botanic Gardens, Kew. https://colplanta.org/taxon/urn:lsid:ipni.org:names:88444-2/general-information
Cactaceae endémicas del Perú. Mónica Arakaki, Carlos Ostolaza, Fátima Cáceres and José Roque, Revista Peruana de Biología 13(2): 193s-219s, 2006. https://www.redalyc.org/pdf/1950/195018608026.pdf
Población y asociaciones de Trichocereus pasacana (Cactaceae) en Los Cardones, Argentina. M. de Viana, N. Acreche, R. Acosta and L. Moraña, Revista de Biología Tropical 38(2B): 383-386, 1990. https://tropicalstudies.org/rbt/attachments/volumes/vol38-2B/04_Viana_Trichocereus.pdf
Distribución espacial de Trichocereus pasacana (Cactaceae) en relación al espacio disponible y al banco de semillas. Marta Leonor de Viana, Revista de Biología Tropical 44(3)/45(1): 95-103, 1996-1997. https://tropicalstudies.org/rbt/attachments/volumes/vol44-3A/13_Viana_Trichocereus.pdf
Echinopsis terscheckii. UA Campus Arboretum, University of Arizona. https://apps.cals.arizona.edu/arboretum/taxon.aspx?id=831
Torch Cacti (Trichocereus hybrids). Arizona-Sonora Desert Museum Plant Care Information. https://www.desertmuseum.org/visit/sheets/TrichoX.pdf