We have a spineless cactus that we planted about thirty years ago in the Southern Arizona desert, purchased as, and appearing to be, Cereus peruvianus monstrose. It has been neglected but the tallest shoot is now ~4m tall, and the past several years it has attempted to bloom.

The flowers make no sense for a Cereoid cactus: there are only a few tepals, the flowers never open, they vaguely appear bilabiate (but that may be an illusion), and the buds are chokingly dense. We've not been able to find any pictures on the web of anything like this. The flowers are too high to pick one to dissect it.

Any ideas? Do you know of a more specialist forum where this question might be asked?

Is it possible that the monstrose type of growth causes poor flower formation? Many cristated Cacti flower poorly.
https://davesgarden.com/guides...

I can't ID the plant and I don't recognize the flowers (very weird) so I'm not sure what's up there. I have a different monstrose version of the Cereus, one that gains and loses ribs, slightly tubercular growth, and it flowers just like the wild type, and produces the same type of fruit (maybe slightly smaller).

It is not a cereus, it is a Totem Pole cactus. The monstrose variety of the Senita. The flowers are completely normal for that cactus. Botanical name: Lophocereus aka Pachycereus schottii var. monstrose.

I will add that these flowers are truly only open at night, unlike the cereus flowers which will be open into the morning, but yes they can be weird looking.

mcvansoest said: I will add that these flowers are truly only open at night, unlike the cereus flowers which will be open into the morning, but yes they can be weird looking.

Arent these distorted though?

I do not think I have pictures of the flowers on mine, but my memory says they looked very much like normal flowers when open, to me most of these look like flowers who are closed after having been open the night before. However, my memory could easily be wrong.

I had some on one of mine earlier this year, but forgot to go outside to get pictures.

To the original poster: I suspect you might be disappointed not to have a cereus with the large flowers, but to most this would be the more desirable plant to have grow large in your yard. The Senita is native to southern AZ, though these monstrose versions originally come from Mexico afaik.

Duh, I'd forgotten there was a monstrose senita. Many thanks for the correction. Here's another picture of a different shoot showing that it's in the process of forgetting its monstrosity and growing with normal ribs; still hasn't recovered the knack of long slender spines, but it's beginning to try, as you can see a few shortish, slender, twisted spines.

Looking at senita pictures I see the buds are normal; mine definitely do not open, and most of the buds fall without reaching full size.

Good to have this resolved before it blows over in a monsoon storm next year!