Pediocactus simpsonii, a small but stunningly beautiful cactus is commonly called "hedgehog" or "pincushion" cactus [those names are also commonly applied to other cacti], but my favorite nickname for it is "mountain ball cactus". This one has always bloomed in the last few days of May into the first week in June - but this year it is two weeks early.
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[I have previously posted images of this particular cactus and called it a "Mammillaria", a closely-related genus. Mea culpa.]