The Garden of Eaden: DINOSAUR PLANTS: The Cycad

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The incredible, yet stunning looking Cycad is so unusual in shape and design that it almost looks unreal. Both visually and literally prehistoric, cycads are found across much of the subtropical and tropical regions of the world. They are predominately found in South and Central America, but cycad species can also be found in Mexico, the Antilles, southeastern United States, Australia, Melanesia, Micronesia, Japan, China, Southeast Asia, India, Sri Lanka, Madagascar, and southern and tropical Africa where at least 65 species occur.

Cycads belong to the biological division Cycadophyta. There are three families of cycads still in existence today - Cycadaceae, Stangeriaceae, and Zamiaceae. While they are only a minor component of the current plant kingdom, during the Jurassic period they were extremely common. Surprisingly, they have changed little since the Jurassic period, especially when compared to other plant divisions which have experienced major evolutionary changes over such a long period of time.

Prehistoric Cycads

The cycad fossil record dates to the early Permian, 280 million years ago (mya), but there is some controversy over some older cycad fossils which appear to date back to the late Carboniferous period, 300–325 mya.

One of the first colonizers of terrestrial habitats, the cycad probably diversified considerably within its first few million years, although the extent to which it radiated is unknown because relatively few fossil specimens have been found. The regions to which cycads are now restricted to probably give a good indication of their former distribution in Pangea before the supercontinents Laurasia and Gondwana separated.

Recent studies have indicated that the common perception of existing cycad species as living fossils is largely misplaced. Although the cycad lineage itself is ancient, most species that are around today have only evolved in the last 12 million years.

The family Stangeriaceae - which consists today of only three species - is thought to be of Gondwanan origin, as fossils have been found in Lower Cretaceous deposits in Argentina, dating to 70–135 mya.

The family Zamiaceae is more diverse, with a fossil record extending from the middle Triassic to the Eocene (54–200 mya) in North and South America, Europe, Australia, and Antarctica, implying that the family was present before the break-up of Pangea.

The family Cycadaceae is thought to be an early offshoot from other cycads, with fossils from Eocene deposits (38–54 mya) in Japan and China, indicating that this family originated in Laurasia. Cycas is the only genus in the family and contains 99 species, the most of any cycad genus. Molecular data have recently shown that Cycad species in Australasia and the east coast of Africa are recent arrivals. The current distribution of cycads may be from just a few ancestral types from Laurasia and Gondwana, or could be explained by genetic drift following the separation of already evolved genera.

Is there a future for the Cycad?

In recent years, many cycads have been dwindling in numbers and may face risk of extinction because of theft and unscrupulous collection from their natural habitats, as well as from habitat destruction.

The Garden of Eaden

DINOSAUR PLANTS: The Cycad

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