What columnar cactus species I should select as a rootstock for a Rhipsalis standard?

Question

I want to make a standard⁽¹⁾ with scions from a Rhipsalis pilocarpa, or mistletoe cactus. I need a rootstock that:

• Is columnar
• Is unbranched
• Has good longevity (at least 20 years)
• Can adapt to high humidity and light shade
• Has a slim, clean, stem at least 3' long

Stem rigidity is optional, because the plant would be staked at about 3' (by the graft union). I will be side grafting.

I have been considering using a freshly rooted Selenicereus cutting as the rootstock. Is that a good choice? If so/no, what other options do I have?

^{(1) Standard in this context means 'tree form', as a standard rose bush. This term is used with plants that do not naturally grow in tree form, trained to one single stem, or 'trunk', resembling a tree, although smaller in size.}

Answer 1

I don't know if you've seen this link, but it's a great resource for comparing rootstocks. http://www.kadasgarden.com/Cgraftingstocks.html

From what I can tell, Cereus jamacaru seems to fit the bill. It is shade and water tolerant, is columnar, reaches 5 meters in height therefore I believe it must have good longevity.

It does, unfortunately, branch.