Lovely plants, Ralph.
How big / old are these? I’m trying to gauge how close some of my seedlings may be to flowering.

Looks fabulous!
How tall is the plant, Tony?

^^ Superb, balanced advice from Karl. The only thing I'd add is to not sow all your seed as a single batch. While you are first starting , the experience curve is very steep, and it's a good option to try something, do it for (say) a month, and then try with more seeds and see if you can improve on ...

That pot seems to sum up my experience, Iann.
Spathulate "pyrodorum" are very floriferous and stay solitary longer, toothy "villetii" don't flower, at all (yet?) for me, but quickly develop into multi head plants.

Some cacti have extrafloral nectary and do exude a sticky substance. I didn't think Melocactus did. Could something have dripped on it? And to really settle things, what did it taste like? Aloe flowers often drip nectar. And, no doubt, many other plants too. Has there been anything in flower above ...

SteveJones wrote: ↑Sun Apr 19, 2020 3:10 pm Rebutia?

That would be my vote. I could guess a species name, based on "small-bodied, with pectinate spines" but wont.

Great, thanks. Lovely flowers. How tall are the stems on yours?
The seedlings sown earlier this year are growing at a rate of knots!

Yes, that's the one.
I used some last year and have just restocked - free delivery if you order 2 bags. No discount with a discount code.
Same day free delivery (for my postcode anyway) arrived the next day...

Another plant that does the same is Peniocereus greggi, if the pot is too small it stops flowering. I'm trying these from seed this year - they seem robust and very fast growing seedlings so far (fingers crossed). How thirsty do you find them? And are they in any way tricky or specific in their req...

I eagerly await rampant growth and flowers each year from my venerable plant. Each year I'm disappointed.
It's a long term survivor of the bonsai treatment. Hopefully a fairly generous repot last year will finally kick in.