It must be Spring! Rain!
Such a tiny cactus usually will be multi-stemmed, but this small mammillaria is generally solitary. And yet it stays under 6″. While the flower colors are variable, we’ve had crops for 2 years in a row with the same flower color.
While these will bloom through the summer, we find that they throw out a few early flowers, sometimes even more than a few, when we have an early spring. And I do mean early.
Oh, and if you click the picture you’ll see the whole plant. All 2 bloody inches of the thing. Click away!