I agree with phil_SK. And please number the pictures, it makes it a lot easier.

So both plants has the field number L 689, but there is also another number, perhaps set by the previous owner to identify the plant in his/her collection? Such numbers are not called "field numbers", one term I have seen is "accession numbers". Alfred Lau was indeed from Germany...

Robinj wrote:with following numbers but different field numbers.

Could you expand on that, please? What is the other field number? And which number follows what? And how can you tell from the field number that it belonged to someone i Germany?

Pilif wrote:that looks like a sulcorebutia

I see what you mean, but are the buds not too hairy and pointy for a Sulcorebutia?

majcka wrote:And why not just call it Echinopsis (and nothing else)? If you don't know the spicies Echinopsis is good just aswell. Is it?

In principle yes (and I sometimes do that on my own plants), but it is common practice to replace the species name, if unknown, with "sp."

Peterthecactusguy wrote:Nope, I mean Echinopsis subspecies which is SSP (S means sub) (SP)ecies.

But what would the species be then? There is no point in calling it "unknown subspecies" as long as you don't know what the higher taxonomical level (species) is.

Peterthecactusguy wrote:Daiv that's why to be safe I call it Echinopsis SSP.

You do mean "Echinopsis sp.", right?

Would the recommendation for that still be to not water it for awhile, let it rest and get some light? I would give it small amounts of water and wait for signs of growth. Actually I would have unpotted it, inspected the roots and repotted the pieces/plants in coarser soil with less peat, waited fo...

Could be an Echinopsis chamaecereus, and if so it is not extremely etioliated, just etioliated and not feeling well .

Agreed. And if it really has lost its roots, exposing it to more light and heat might stress it even further.

iann wrote: I've never seen them on Opuntioids

I have, but very seldomly.

My guess is a fungal infection that already has destroyed much of the plant (beneath the skin). Watch it carefully over the next week, if it spreads further the plant is doomed.

Robinj, what are you using as growing medium?

Robinj wrote:The thermostat, it is a problem. It intentionally drops the room temparature to 16 degree's celsius.

I have often sown cactus seeds when the temperature has gone down to 17-18 °C at night, and they have germinated well, so I am not sure that it is a problem .

I would say it depends on exactly what you intend to use it for, and how. Some terrarium owners think that planting some cacti in the shallow sand together with lizards under terrarium lamps is a good idea. It is not. It sounds as if you intend to use it exclusively for cacti, perhaps growing them f...