Cycads and cycadeoids

Cycads and the extinct Cycadeoids (Bennettitales) are closely related gymnosperms. The basic difference between the two is that cones occur at the apex top of the stem in living
cycads [Figure 1], but are embedded among the leaf bases in cycadeoids [Figure 2].

Cycadeoids are easily recognized by the diamond-shaped leaf bases of the trunk.  In many well-preserved specimens, you’ll see the cones of a Cycadeoid among the leaf bases.

Figure 1. Cycadalean structure (from Tidwell, 1998)
Figure 2. Cycadeoidalean structure (from Tidwell, 1998)
Bennettiales from the Sedgwick Museum’s collection. Note the “cone” in the top-right of the image, and leaf traces. Width is ~15cm.