Oldest cactus fossils

There are very few remains of cacti in the fossil record making them one of the most difficult groups of plants to age in terms of their origin. The oldest traces of cacti discovered are the fossilized seeds and spines of pricklypear plants (Opuntia spp.) found in the dung heaps (middens) of packrats (genus Neotoma) in what are now desert and brushland areas of North America that have been radiocarbon dated up to 30,800 years old.

It was believed that a fossilized cactus named Eopuntia douglassii, dated to the Eocene period, some 40 to 50 million years ago, was discovered in the Green River Formation in Utah, USA, in 1926 by collector Earl Douglass, however this was later confirmed to be a specimen from an unrelated plant family.

It has long been accepted that cacti's near-exclusive native distribution to the Americas is evidence that these plants had to have emerged after the splitting of the ancient supercontinent Gondwana, which separated Africa and South America, some 140 million years ago in the Early Cretaceous period. Although difficult to pinpoint their origin after that owing to the limited fossil evidence, molecular studies indicate that the first cacti most likely emerged between 30 and 35 million years ago.