Cycadophytes - the True Cycads

These two cycads from the MSU Botany Greenhouse demonstrate the palm-like nature of cycad foliage.
 

If the plants are in reproductive condition, there is no possibility of confusing them with palms. Palms are flowering plants that bear small, inconspicuous, wind-pollinated flowers. Cycads are gymnosperms a bear large, conspicuous cones. In this case, the plant bears an immature ovulate cone. The ovulate cones are typically very large and even the pollen cones are larger and more persistent than are the equivalent male cones of conifers.

Although significant elements of Mesozoic vegetation, cycads today are represented by only 10 genera, confined to the semi-arid tropics and subtropics. Mexico presently has the highest diversity of living cycads. All extant cycads grow very slowly and the cones can take several years to mature. The plants are thus quite vulnerable to predation and have evolved a number of different defenses. The trunks, leaves, are cones are often densely covered with stiff, sharp spines which serves to deter larger herbivores. They also produce an amazing array of toxic alkaloids which serves to limit insect predation.

A reconstruction of Leptocycas, an early cycad from the Upper Triassic (Delevoryas and Hope, 1971). Other than a relatively smooth trunk (between 1 and 2 meters in height), this plant looked remarkably like modern cycads, especially with respect to its leaves. Other Mesozoic cycads were less typical in this respect and some, like Bjuvia, had entire leaves!
 

While the cones of Cretaceous and Tertiary cycads were quite "modern" in appearance, the cones of Jurassic forms were far less so. An ovulate cone of Baenia is shown on the left, demonstrating a very open structure that provided very little protection for the ovules, one of which is shown in cross-section at (C) to the upper right. The lower right (B) shows a cone of Androstrobus, a pollen cone, with small pollen sacs visible behind the cone scales. (Jurassic, Stewart, 1983).

In terms of diversity, the cycads have been in decline since the late Mesozoic, probably as a result of the failure to compete effectively against Angiosperms except in relatively dry habitats.