Cycads

Ecology & Form

• Palm-like gymnosperms, inhabiting tropical (moist and arid) environments

Stems

• • Usually possess a single trunk 

  • Eustele w/ cambium to produce small amounts of wood

    • Wood production is polyxylic; forming successive cambia

  • Manoxylic wood 

  • Largest pith in plant kingdom 

  • Leaf traces that wrap around cortex (girdling) 

Leaves

• • Fronds; large pinnately compound leaves

  • Many are rigid and tough

  • Possess hypodermis to prevent water loss 

Roots

• • Above ground roots that look like coral (=coralloid) 

  • These roots contain cyanobacteria

Reproductive Structures

• Dioecious (separate male and female plants)

• Large ♂ and ♀ cones

  • simple cones (=born on modified leaves)

  • Pollen sacs on male modified leaves (=micro-sporo-phylls)

  • Seeds on female modeified leaves (=mega-sporo-phylls)

• Beetle pollination 

• Cone-like in many families

• Largest sperm cells in the plant world; zoidogamous (sperm swim to egg)

Cycadodendron galtieri

• Luthardt et al. 2023

• Early Permian of eastern Germany

• Slender stem with wide parenchymatous pith 

• Primary vascular system consisting of densely arranged interconnected medullary bundles scattered throughout the pith and circularly arranged bundles in the pith periphery 

• Metaxylem tracheids of vascular bundles with multiseriate-bordered pits 

• Successive vascular segments with centripetal xylem and centrifugal phloem 

• Innermost vascular segment with distinctly wider primary rays compared to the outer segments 

• Wide-lumen secondary xylem tracheids with araucarioid-type pitting 

• Medullary bundles obliquely traversing the vascular segment(s) through primary rays 

Right: Sketch of cross-section of stem (Luthardt et al. 2023; Figure 4)