[http://en.wikipedia.org/wiki/Apple] There are more than 7,500 known cultivars of apples resulting in a range of desired characteristics. Cultivars vary in their yield and the ultimate size of the tree, even when grown on the same rootstock. In the wild, apples grow quite readily from seeds. However, like most perennial fruits, apples are ordinarily propagated asexually by grafting. This is because seedling apples are an example of "Extreme heterozygotes", in that rather than inheriting DNA from their parents to create a new apple with those characteristics, they are instead different from their parents, sometimes radically. Triploids have an additional reproductive barrier in that the 3 sets of chromosomes cannot be divided evenly during meiosis yielding unequal segregation of the chromosomes (aneuploids). Even in the very unusual case when a triploid plant can produce a seed (apples are an example), it happens infrequently, and seedlings rarely survive. Most new apple cultivars originate as seedlings, which either arise by chance or are bred by deliberately crossing cultivars with promising characteristics.

OK, so I am saying that maybe these Peruvian sacred cactus seeds are also unpredictable. There is no commercial interest in sacred cactus so no one is spending millions of dollars to research their genetics. We can assume that people valued trichocereus for thousands of years, propagated them by cuttings based on the particular traits they liked. They fall over naturally and self root; any fool can figure that out and did for thousands of years. Growing them from seed is almost unnatural. In 20+ years I have never encountered San Pedro spontaneously growing from seed.