Questions for Further Thought

1. Among the earliest representatives of the fern and sphenopsid clades are plants that possess characters that would ally them to both lineages. Much energy has been expended arguing over which characters are most important and therefore to which clade a given plant belongs. What other interpretations of this observation are possible? Explain.
2. Most paleobotanists classify Sphenophyllum with the sphenopsids. Clearly this choice reflects more emphasis given to some features than others. From what you know about evolutionary process and the origin of the various structures, do you agree with the conventional wisdom? Why or why not?
3. Ibyka has often been tied to Hyenia and Calamophyton. In your opinion where do you want to put these two genera, based on what you know about sphenopsids, ferns and Ibyka?
4. On what basis would you argue that Rhacophyton is a "true" fern - or not? Consider the hypothesized origin of leaves and synapomorphies of ferns that you know of.
5. Salvinia, Azolla, and Marsilea are all aquatic AND heterosporous. Keep this in mind when reading about the origin of seed plants next week. Is there a relationship between these two characters, and if so, what? HINT: Read a bit more about the ecology of heterospory, for example, Phillips and DiMichele (1992) and DiMichele, Davis and Olmstead (1989) in your reader.
6. What are the differences between the evolutionary histories of sphenopsids and ferns, respectively? How do they differ in ecology? Any relationship?

[Previous Page] [Title Page] [Glossary] [Range Chart] [Geologic Time Scale] [Next Page]

---