The darker brown spines are fresh and young, which is an indicator that is growing. Cacti(like this one), cactus like euphorbias and stapeliads, all grow their stems from a grow tip, near the apex of the plant. If they branch, or grow pads, they do it from special (universal) organs called areoles, which are unique for cacti. Euphorbias and stapeliads lack these wooly, spiny dots.

These areoles emerge from the apex, along with parts of cactus called ribs, with new spines, and will be pushed down and sideways as growth progress.

My best example would be a ferocactus hystrix that i grow from ping pong ball(not mine, just for reference):

https://www.giromagi.com/prodotti/thumbs/ferocactus_histrix_23129.jpeg

to this thing..

https://garden.org/plants/photo/551397/

Which is bigger than a tennis ball, at 6 years in care. Plant was donated...

Over time, this is how an adult looks like

https://garden.org/plants/photo/578066/

A lot of cacti dont have a fast growth speed, or grow in any noticable manner(branches, pads etc).

Your cactus is a young specimen belonging to the genus melocactus, which(when mature) exhibit a unique inflorescence called a cephalium. The cactus stops growing then, while the cephalium does...

Thanks for that helpful information! I have another cactus doing something similar. This one looks more like a flower

Hello ,

was hoping for your advise with this one again. Within the last few days one of the white patches where the thorns grow out of has turned black. Any suggestions? It has rained a few times. Some of my other plants have gotten sunburnt in the last week. Not sure which.

Black spots are mildew. Dilute bleach(a lot) and clean with brush..