Species
Knuthianus
What growers report of its look, the published name, where it has been collected, and what is sold under it.
What growers report
One grower describes a knobbly profile, and a strain in their own collection carrying unusually long spines of the kind you would expect on a bridgesii.
The name
The International Plant Names Index records Trichocereus knuthianus Backeb. as a validly published name, first published in 1937. Reportedly, the Caryophyllales Network, the working taxonomy for the cactus family, does not keep it as a species of its own: it is carried in the synonymy of Trichocereus cuzcoensis.
Where it grows wild
It has reportedly been collected in the wild on the Rio Maranon in Peru.
What the name covers
At least two distinct plants are reportedly sold under this name, from different countries and from different growers.
What that means when you buy one
A plant labeled knuthianus tells you which epithet the seller reached for. On its own it does not tell you which plant you are getting.
Names in the library
A clone name is not proof of a species, and a photograph is a pointer rather than an answer.