CactiGuide.com

I have lost my identification of this one. Cleistocactus smaragdiflorus? Never flowered unfortunately.

Smaragdiflorus seems like a good match, although Cleistocactus hyalacanthus ssp. tarijensis may be a possibility also. Flowers will definitely resolve the mystery.

Thanks! Yes, they both seem to fit. Will wait for flowering (it was bought 5-6 years ago as a young plant so it is not much older, now it is about 40cm high).

While repotting, the old seller's label was found buried in the soil. According to this label, the seller identified it (tentatively - with a question mark) as C.brookeae v.flavispinus (listed just as C.brookeae in many sources). To me, C.hyalacanthus or C.smaragdiflorus still look more likely as this cactus has quite distinct central spines which C.brookeae lacks.

Definitely not C. brookeae; however, Lucy_V's suggestions are both good. I personally lean towards C. smaragdiflorus as C. tupizensis centrals tend to be a bit more brownish and not as golden, but certainly within potential variability.
Can't wait to see the flowers!

C. brookeae (syn. C. wendlandiorum) is quite a different plant, the spines looking more like C. straussii, but can be white ot have a slight yellowish tinge. However the flowers are completely different being bent like a tea or coffee pot spout. As said in the link below, whether the stems grow upright or eventually hang down the flowers still bloom with the bend the correct way up, as does it's relation C. vulpis-cauda which tends to become pendulous even quicker. No doubt if the flowers did not orientate themselves independent of the stems the nectar would fall out when the stem became pendant?

See:-

http://forum.bcss.org.uk/viewtopic.php?f=1&t=161912

It finally flowered this year, and I am now quite certain it is Cleistocactus hyalacanthus ssp. tarijensis. It is quite a nice plant now, with 2 stems still going in parallel (now circa 70cm high), and 2 smaller ones continuing the growth.

I think you nailed it!
Beautiful plant!

I noted very big differense in size between C straussii and C hyalacanthus in my collection. The second one is much smaller and tiny.
PS What plant to the right on the last pic? Stenocereus - ?

Our C.straussii with 3 branches is not much higher, but the branches are thicker.
To the right is Pachycereus pectin-aboriginum from the local plant shop (cutted branch top), grows quite irregularly, this year has yet to start. Last year it did better: