Red fruit on a mound of mammillaria cacti
D167-2015 One of the Pincushion or Mammillaria cacti in the collection.
From the color of the cactus flesh, the nature and distribution of spines, etc., I am guessing it is Mammillaria #06, for which no species ID is known.
Conservatory, Matthaei Botanical Gardens, Ann Arbor
Taken June 16, 2015; edited 2017
From Xeric Plants Through the Year