Trichocereus... I think.. Not weird, rather common..
Bill in SC

No its not that, there is only three sides and they go in and all three of them meet in the middle, so if i took a cutting from it, and looked at it from the top it looks kind of like a star with three things that all meet in the middle, the middl eis very skinny.

I soooo think I am all over this question! How about this guy. Yours might not have the roots growing from the sides of the plant, but many do over time.

Harrisia martinii

{{gwi:738519}}

Travis

Hylocereus, usually undatus. Grows upto 6' per year and very cold tender. Not the best for grafting, short lived, but cheap. Better for long life are Trichocereus spachianus, Myrtillocactus geometrizans or even just Cereus peruvianus. For just quick growth, a better stock plant would be Pereskiopsis.
What is the scion plant (top)?
Dan

Hey, no sorry guys, lol, but this cactus hase really small black thorns that are really stiff. they dont hurt that much.

Euphorbia trigona?

Here is a link that might be useful: Euphorbia trigona

finally, it lookes sort of like that without the ribs, and the leaves.

Helo botanist:
Do not try to graft cacti over it, because they are different species. The Euphorbia has spines but they are not Cactaceae.
Alfonso

hey i got a weird cactus too. it's round and flowers little white furry things. thorns hurt

I've got a root stock that I got from a nursery where the grafted plant died and the stock just took off. It has the triangular shape and the roots, but no spines. Does anyone have any clue?

Dear DC,

Google Hylocereus undatus (a common stock (bottom) for the scion (top) in grafted plants).

Harrisia: What a great watercolor! Did you do it yourself?

Euphorbia triangularis is my guess. If this is your plant, you can't graft a cactus onto it. It will die, die, die. And then it will die some more.

But they are pretty plants all on their own...

YEA THATS IT. finally, so i shouldnt graft to this

That is a Euphorbia. It is not a cacti. You can't graft a cacti to a euphorbia because euphorbias are not cacti, and cacti are not euphorbias. It is just a euphorbia that looks like a cacti but is not realy one at all. If you cut it, white sap will come out. I think all euphorbias have the white sap and no cacti have white sap. That's one way to check if it is a cacti or not.

beautiful euphorbia lactea....great job

bongo monkey,

some cacti accually have white sap even if most don't.

/David