It looks like Austrocylindropuntia subulata.

Cacti are succulents too. (All cacti are succulents, but not all succulents are cacti).

Weekly watering may or may not be OK - both plants looks OK, are they potted in same container? - it very much depends on how well the potting mix dries up and drains, how warm it is where the plants are and how much light they receive. And some species will like watering bit (not a lot) more often than others.

It looks like some member of the Opuntia group..I am sure other will chime in with a species name for you.

Not sure why you think watering frequency determines if it is a cactus or not? Cacti ARE succulents..

haha Rina,we were typing at the same time!

That is great plant Harry!

Is it different species - maybe Austrocylindropuntia cylindrica? (IIRC, there are about 10-12 sp?) Trunks are so smooth comparing to most photos (and my own plant)....

Could be Rina. I don't know. Eventually it became so big that I cut off most of it.

here are some more pics.

Somebody - I forgot - liket it so much that he/she would have it. Never heard how it ended.

Thanks for the replies all. Your suggestions are close but it's very hard to tell because my plant is so much smaller than the suggestions. There's less variation of colour and texture between the parts of the plant (tops vs trunks) on my plant too and the spines aren't sharp but that may be because of its size/age.

Whitney

My plant is just a little bigger than yours.

I would dare to say that it is Austrocylindropuntia, most likely subulata. You can google photos of each species (about 10?-11? 12?) and compare.

Color will vary a lot depending on light succulents get - so the color alone will not be sure way to correctly ID any plant. In low light, plants will also grow skinnier, longer/taller and often spindly stems. If they have leaves, they are usually too far apart. So the plant could look totally different than it should (I am not saying yours does). Even old/mature plant grown under not-so-suitable conditions will not look as it should.

Whitney, the green spikes on your plant are leaves. Some cacti grow leaves. Also, I can see some spines next to the leaves in your picture. Your cactus is an Austrocylindropuntia but I'm not sure which one. It looks like a frequent branching cultivar I've seen in stores. It might be a cultivar of A. subulata.

Correction: it's the monstrose form of A. subulata