OMG! a normal pereskiopsis plant is shown on the right of the huge one with 'gigantism'.
i think we need to get hold of some of this for grafting! imagine the growth rate!!!
from site:
http://translate.google.com/translate?hl=en&sl=pl&u=http://www.kaktusy.com.pl/pliki/kurioza/chimery.html&sa=X&oi=translate&resnum=3&ct=result&prev=/search%3Fq%3Ddigitostigma%2Bx%26start%3D20%26hl%3Den%26sa%3DN

That... can't be right.

Imagine what that would do to a scion!

looks normal, what's special about it? when grown in ground, outdoors
in good conditions, they will grow much larger than that. they create
shrubs/bushes/hedges etc when older.

normal? nothing on that site is normal...

I too would consider it normal. They get pretty big like Kada said and they get massive sharp spines on them too, with these and the glochids it's hard to believe they are so popular. They their uses though and for this they can be forgiven lol

I certainly recognise that they indeed are big - sometimes it's easy to forget that Pereskiopsis exists in a form other than as an 8-inch cutting with a fragile Mexican species grafted to the tip... however, in this case the size of the plant and the growth pattern surprised me. Normally, to see a stem of that size you'd expect some branching to occur. This specimen has just grown straight up.

^yep. because its got something wrong with it.. 'gigantism'.
on the site there is the same thing with Opuntia subulata.

There are other species too I believe...that might be the answer right there

It certainly looks big to me

ya many cool things on the site, but i just dont see anything but a big peresk there.

try growing one in a big pots with good rich soil, high humidity full sun and 30C, you will get the same thing Pereskiopsis vary GREATLY just due to the environment