This was a great example of how you always find other cool plants when doing work on studying others. When looking at some Hechtia plants in Queretaro, Mexico I stumbled on these wonderful little cacti that also happened to be in full bloom!
These Strombocactus disciformis are rather small cacti grow in an interesting way, on vertical walls between crumbling and decomposing stone.
Between their size and color they are very tough to spot. Which is probably a good thing as like many other rare cacti there is a lot of pressure from extraction which can easily decimate a population. And when plants are limited to very specific places where they can grow, it makes them very vulnerable.
Here is a picture to give a better idea of the size of the plants and the flowers. If you look closely, you can see dozens of young plants. Amazing thinking about how the seeds can hold on and start growing on this vertical surface!
Here is a more broad view of the plants and one of their companions, Agave xylonacantha.