7.1: Cycads

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

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.

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.

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.

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.

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.

Figure \(\PageIndex{6}\): From the megastrobilus, seeds are produced. The large red seeds can be seen still within the feathery megasporophylls of this megastrobilus. Cycas revoluta, photo by Kylelovesyou, CC BY 3.0, via Wikimedia Commons.