Flower:

1 to a few flowers emerge from the apex of the ball, appearing in sequence over the blooming period. Flowers are showy, funnel-shaped, to 2 inches long and 1 to 2 inches across, with many hot pink to magenta petals and a ring of flourescent orange-tipped stamens surrounding 9 soft white fingers that make up the stigma.

Leaves and stem:

With cactus, the fleshy body is a modified stem and spines are modified leaves. The stem is oval to ball-shaped, 1 to 5 inches tall and 1½ to 2 inches in diameter covered with raised bumps called “tubercules”. A radial array of about a dozen ¼ to ½-inch whitish spines is at the apex of each tubercule. 3 to 8 brownish spines up to ¾ inch long project up and out, effectively armoring the space between tubercules. Each tubercule has a groove on one side, though it is sometimes faint. Plants grow singly or in small clusters.

Notes:

Pincushion Cactus can be numerous on accommodating sites on the Great Plains from the Dakotas west, even surviving well in rocky pastures, the balls nestled into the short grazed grasses. Size makes it difficult to spot when not in bloom. A similar species is Escobaria missouriensis (nipple cactus), which has yellowish flowers and no grooves on the tubercules. This species also goes by Coryphantha vivipara (perhaps more commonly so) but Escobaria vivipara is the accepted name in Minnesota. I found 1 reference that explains the seed and flower morphology that put it in Escobaria, where it's been accepted since 1923.

Unfortunately the cultivated specimen shown in Additional photos below appears to have been uprooted by some mangy pest (opposum?) that then consumed the fleshy barrel from the roots leaving the armored cuticle behind.