Both of these fossil stems have typical cycad stem anatomy, including a small amount of manoxylic wood, a broad pith, and resin canals. Cycadaceous foliage such as Nilssonia is a common component of Mesozoic floras in both the northern and southern hemisphere. See the figure on p. 347 of your text for a general idea about the structure of this foliage. Cycadeoideales Along with the cycads a second fossil group, the cycadeoids, produces what has been called cycadophyte foliage. However, cuticular studies have demonstrated that these two groups can be distinguished from one another on the basis of epidermal and stomatal differences.
Cycads have epidermal cells with straight margins, thin cuticle, and irregularly oriented stomata.
Generally, cycads, conifers, seed ferns, Ephedra , Ginkgo , and the angiosperms all have haplochelic stomata, where the guard cells of the stoma develop from one epidermal initial and the associated subsidiary cells from another initial. Cycadeoids are also characterized by epidermal cells patterns with wavy margins, thick cuticles and cells aligned in rows, and stomata occurring at right angles to the veins. Cycadeoid foliage is a common component of the Triassic Chinle Formation, the Triassic rock formation of the Petrified Forest National Park, Arizona. Look at two representatives of this foliage Otozamites and Podozamites , in the lab. You can see how this foliage would be easily assigned to cycad-like plants, based on its similarity to that of living cycads.