Another cactus flower is open today, Chamaelobivia. This is an intergeneric hybrid between Chamaecereus and Lobivia, although both these genera have been lumped into Echinopsis now. So I guess this is just a plain old Echinopsis hybrid.
It doesn't matter what it's named- isn't it gorgeous.
This is about as tall as the plant will get, but it will form a clump of stems over time.
[Note to self: You have not adequately planned ahead for when all your plants grow and get bigger over time.]