7.1: Cycads

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Cycads are one of the more ancient gymnosperm lineages, appearing in the fossil record around 300 million years ago. Currently, many extant species are in danger of extinction in the wild. However, during the Jurassic period, these plants would have dominated the landscape. Though their large, compound leaves make them appear to be ferns at first glance, cycads can be classified as gymnosperms by the production of seeds instead of spores and xerophytic leaves. These plants share the following features:

Dioecious. Male and female strobili on separate plants.
Large compound, xerophytic leaves
Insect pollinated

A cycad that has many fern-like leaves (long and pinnately compound) seeming to emerge from a central point — Figure \(\PageIndex{1}\): The first image is what might be considered a "typical" cycad. The leaves are long, tough, and pinnately compound with long, thin leaflets. Unlike a fern, the leaves look tough. The plant in the second image also shares these characteristics, yet it might not immediately stand out as a cycad. First: *Dioon* *holmgrenii,* photo by Daniela Fernandez y Fernandez, CC-BY-NC. Second: *Bowenia spectabilis,* photo by kerrycoleman, CC-BY-NC.

A plant with shiny, long, pinnately compound leaves, but the leaflets are wide, not long and skinny — Figure \(\PageIndex{1}\): The first image is what might be considered a "typical" cycad. The leaves are long, tough, and pinnately compound with long, thin leaflets. Unlike a fern, the leaves look tough. The plant in the second image also shares these characteristics, yet it might not immediately stand out as a cycad. First: *Dioon* *holmgrenii,* photo by Daniela Fernandez y Fernandez, CC-BY-NC. Second: *Bowenia spectabilis,* photo by kerrycoleman, CC-BY-NC.

A small arborescent cycad with a distinct trunk, leaves emerging at the top to form a crown — Figure \(\PageIndex{2}\): A cycad taking an arborescent form. It has a distinct, woody trunk and the leaves are emerging from the top of the trunk to form a small crown. Cycas ophiolitica, photo by Geoffrey Sinclair, CC-BY-NC.

A close up picture on the leaflets of a cycad — Figure \(\PageIndex{3}\): Each leaf blade shown here is a leaflet from the larger, pinnately compound leaf. There are many parallel veins of vascular tissue traversing each leaflet and the rachis of the leaf looks woody. Zamia integrifolia, photo by John C., CC-BY-NC.

A single, large, central strobilus with small scales spiraling around it — Figure \(\PageIndex{4}\): The large microstrobilus, the pollen-producing cone. This structure would be produced on a "male" plant and consists of many microphylls bearing microsporangia. It is called a microstrobilus, not because it is small, but because the pollen (and sperm inside the pollen) produced inside it are smaller than the seeds (and eggs) produced by in the megasporangium. Microstrobili are often larger than megastrobili in cycads. First: *Encephalartos villosus*, photo by Cultivar413 from Fallbrook, California, CC BY 2.0, via Wikimedia Commons. Second: Photo by BillyH, CC BY 3.0, via Wikimedia Commons.

A cycad megastrobilus — Figure \(\PageIndex{5}\): A megastrobilus is composed of overlapping megasporophylls. Cycads are dioecious, meaning male and female strobili are produced on different individuals. These individuals are "female" and so produce a megastrobilus. Inside the megastrobilus, seeds are produced. These are visible in the second photo, the bright red structures that appear to be bubbling up from under the green megasporophylls. First: *Dioon* *merolae* Photo by Raul Ezequiel Gonzalez Trujillo, CC-BY-NC. Second: Macrozamia macleayi, photo by Blawson, CC-BY-NC.

A large strobilus with green megasporophylls and bright red seeds — Figure \(\PageIndex{5}\): A megastrobilus is composed of overlapping megasporophylls. Cycads are dioecious, meaning male and female strobili are produced on different individuals. These individuals are "female" and so produce a megastrobilus. Inside the megastrobilus, seeds are produced. These are visible in the second photo, the bright red structures that appear to be bubbling up from under the green megasporophylls. First: *Dioon* *merolae* Photo by Raul Ezequiel Gonzalez Trujillo, CC-BY-NC. Second: Macrozamia macleayi, photo by Blawson, CC-BY-NC.