Identify this cactus

[UmmH]

Can someone tell us its name? It's grown a lot since we got it and I'd like to know more about it so DC can care for it properly.

We have one of those, the tentacles are so weird, they seem to grow new ones, drop off and continue growing on the windowsill. I love it!

No idea what it is called though, sorry.

Yes! And it seems to change overnight. Do you give it lots of water or a little?

I’m going to guess it is Chamaecereus silvestrii aka the peanut cactus. Whatever it is, it’s extremely etiolated (stretched because of too little light).
It should be in the sunniest place you can put it, but do it gradually, so it doesn’t scorch. Grow in a gritty potting mix, and water only when quite dry ( about once a week in summer, much less in winter). The elongated stems won’t return to normal, but it should produce more stems which are more compact with plenty of light.
Grown properly, it produces lovely scarlet flowers in summer.

Tarantula cactus?

And I agree with PP it needs more light.

Mine has never grown flowers. I water it once a month, if that. It is in a sunny position though. Even when limbs have dropped off they don't die, it's bizarre.

I’m going to guess it is Chamaecereus silvestrii aka the peanut cactus. Or Aporocactus flagelliformis. Chamaecereus sylvestris has its spines in rather obvious straight lines.

Either way - it's not getting enough light, as Nan says. The ends of the branches should be just as thick as the bases, and at this time of year it should be covered with the remains of the copious display of big pink (Aporocactus) or orange (Chamaecereus) flowers earlier in the summer.

You can stand it outside in a sunny spot in the summer, but bring it back inside in September.

Yes, it could be Aporocactus, MereDint, but it’s not often seen for sale these days, which was why I thought Chamaecereus. Whatever it is ,it’s desperate for more light.

Thanks, all. It's in the sunniest spot possible. I usually have it behind the net curtain in the daytime. That pic was taken after it had been repotted, so maybe that's why it looks a bit limp? It's only a few months old, so not flowered yet. Glad to know we chose the right potting mix, and I'll watch out for too frequent watering. I might put it out in the garden so it can get some all day sun, so long as I remember to bring it in again in the evening. With one plant I forgot and a cat peed on it :(

I'm torn between Aporocactus and Chamaecereus. As this pic shows, it's growing in a segmented way, and it's quite floppy...

Be careful exposing it to bright sun outside, after being indoors it could scorch easily, as the growth is very soft, so do it gradually.
Indoors, keep it behind the net curtain so that it gets maximum light, it’ll be easier to ID it once ‘normal’ growth resumes.

That pic was taken after it had been repotted, so maybe that's why it looks a bit limp? It's not the floppiness that's causing Nan and I to say it needs more light, it's the way the branches start out fat and get thinner (as a result of trying to grow rapidly to where there's more light).

If you put it out in the garden, you don't need to bring it in at night. Keep an eye open for slugs - the growth is very soft, so they will be attracted to it, although they don't go for most cacti. I doubt whether it'll be first choice for cat pee.

It's only a few months old, so not flowered yet. I find that very hard to believe. Cacti would struggle to get beyond pea sized in the first year from seed. And that plant is certainly large enough to flower.

@NanTheWiser Could it be something more improbable and even more desperate for light? I've seen lobivias get that long thin growth when starved of light, though I'd find it difficult to believe they'd have the energy to produce that many heads if they weren't getting enough light.

Chamaecerus to my mind has a more ribbed look to it, and more constrictions in the stem - it was the latter attribute that sent me to Aporocactus.

You need to water them more often than you think if you want them to thrive and grow. They will survive if you ignore them but they wont thrive.

MereDint, I doubt it would be anything else, but I think you may be correct in thinking Aporocactus, looking more closely at the areole arrangement, we will only know when it starts to grow normal stems.