This page is about a naming puzzle, not a different plant: "Echinopsis pachanoi" and "Trichocereus pachanoi" are two scientific names for the exact same cactus, the one commonly called San Pedro.
This page is about a naming puzzle, not a different plant: "Echinopsis pachanoi" and "Trichocereus pachanoi" are two scientific names for the exact same cactus, the one commonly called San Pedro. The "syn." in the title is short for "synonym," the botanical term for a name that points to the same plant as the currently accepted name. [https://en.wikipedia.org/wiki/Echinopsis_pachanoi; https://trichocereus.net/trichocereus-pachanoi-britton-and-rose-1920-echinopsis-pachanoi/]
Botanists later decided the genus Trichocereus was not distinct enough to stand on its own and folded it into the older, larger genus Echinopsis. When a plant moves to a new genus its species name comes along, so Trichocereus pachanoi became Echinopsis pachanoi (formally "Echinopsis pachanoi (Britton & Rose) H.Friedrich & G.D.Rowley"). Same plant, new genus label. [https://en.wikipedia.org/wiki/Echinopsis_pachanoi; https://powo.science.kew.org/taxon/77125731-1]
In 2012, botanists Albesiano and Kiesling reorganized this group again and treated San Pedro not as its own species but as a variety of another, as Trichocereus macrogonus var. pachanoi (a "variety" is a rank below species, for a regional form rather than a separate kind). This is why you may also see San Pedro under that longer name. [https://en.wikipedia.org/wiki/Echinopsis_pachanoi; https://powo.science.kew.org/taxon/77125731-1]
All these names are linked because they share the same original Ecuador type specimen; names tied to the same original specimen are called "homotypic synonyms." Ordered from the basionym (the original 1920 name): Trichocereus pachanoi -> Cereus pachanoi -> Echinopsis pachanoi -> Trichocereus macrogonus var. pachanoi. Every link is the same physical plant relabelled. [https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:88444-2; https://en.wikipedia.org/wiki/Echinopsis_pachanoi]
So which name is "correct" now? Kew's Plants of the World Online (POWO), the database many botanists treat as the global reference, lists Echinopsis pachanoi as the accepted name as of late 2025, and files Trichocereus pachanoi and Trichocereus macrogonus var. pachanoi as synonyms of it. Bottom line: Echinopsis pachanoi is the current official name; the others are valid older names for the same plant. [https://powo.science.kew.org/taxon/77125731-1; https://en.wikipedia.org/wiki/Echinopsis_pachanoi]
Growing & propagation
The practical upshot for growers: the very same San Pedro cactus is sold under several names at once, most often "Trichocereus pachanoi" in the nursery trade but also "Echinopsis pachanoi" on botanical labels. A different name on the tag does not mean a different plant, so do not pay a premium expecting something rarer. [https://en.wikipedia.org/wiki/Echinopsis_pachanoi; https://trichocereus.net/trichocereus-pachanoi-britton-and-rose-1920-echinopsis-pachanoi/]
History
The plant was first formally described in 1920 by botanists Nathaniel Britton and Joseph Rose, who named it Trichocereus pachanoi. That original published name (the "basionym," meaning the base name everything later is built on) appeared in their book The Cactaceae, volume 2, on 9 September 1920. [https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:257116-2; https://www.ipni.org/n/257116-2]
The species name "pachanoi" honors Abelardo Pachano, an Ecuadorian who helped collect the original specimen. That first reference specimen (the "type") was gathered near Cuenca, Ecuador. The name has always pointed back to that one collection, no matter which genus the plant was later filed under. [https://trichocereus.net/trichocereus-pachanoi-britton-and-rose-1920-echinopsis-pachanoi/; https://en.wikipedia.org/wiki/Echinopsis_pachanoi]
