The Cycadaceae and Zamiaceae

The Cycads and Coonties


Cycas revoluta	cycad strobilus

The Cycadaceae and Zamiaceae are families of the Cycadophyta with a primarily tropical/subtropical distribution. The Cycadaceae are composed of only a single genus, Cycas,with about 20 species, whereas the Zamiaceae are composed of around 8 genera and approximately 110 species. The Cycadaceae are thought to be the oldest extant lineage of cycads and apparently are the sister group to all other cycads. Cataphylls, cycasins, and coralloid roots are synnapomorphies for the two families and distinguish the cycads from other gymnosperms. Recent molecular evidence (see Donoghue and Doyle, 2000) demonstrates that Cycadaceae and Zamiaceae may well be part of a monophyletic gymnosperm lineage (Chaw et al., 2001), though definitive support for this is not yet available.

Click here for a distribution map of the Zamiaceae in the U.S.A.

Vegetative Characters

each leaf is pinnately compound
several to many leaves are produced per year
the stems are woody, short, stout, and full of storage tissue
coralloid roots with cyanobacterial associations
cataphylls = small leaves at base of other leaves that presumably form protective function
in Cycadaceae the leaflets have circinate vernation, whereas in Zamiaceae they do not

Reproductive Characters

Cycadaceae have only male strobili, the female reporductive structures do not form a true strobilus
Zamiaceae produce both male and female strobili
The strobili of Zamaiceae are large, woody structures with hexagonal, peltate sporophores
Pollination is completed via beetles

Diagnostic Characters

the main synapomorphy for Cycadaceae = female cone scales do not form a strobilus
the main synapomorphy for Zamiaaceae = the large, woody strobili and large seeds (2-4 cm)
cycasins, cataphylls, and coralloid roots are all synapomorphies that deomstrate the monophyly of the three families of cycads
distinctive sympleisiomorphies = seeds, pollen, motile sperm

Economic Importance/Fun Facts

they are commonly cultivated in warmer climates and greenhouses :)
the stems and seeds of some species have been used as a source of starch

Evolutionary Adaptations and Relationships

Order Cycadales
clearly monophyletic
sister group to other gymnosperms
within family relationships determined by rbcL, , and morphological data ().

Glossary of Terms

circinate vernation - the coiling associated with young fern leaves (and here with Cycasleaflets)
coralloid roots - roots that have cyanobacteria living symbiotically inside, resemble coral in shape
cycasins = poisonous glycosides (toxic compounds) that are produced by all cycads
extant - alive on Earth today (opposite of extinct)
sister group = the groups most closely related to the group of interest
strobilus = a cone-like reproductive structure

References and Links

Chaw, S. M., C. L. Parkinson, Y. Cheng, T. M. Vincent, and J. D. Palmer. 2001. Seed plant phylogeny inferred from all three plant genomes: monophyly of extant gymnosperms and origin of Gnetales from conifers. Proc. Natl. Acad. Sci. USA
Donoghue, M.J. and J. A. Doyle. 2000. Seed plant phylogeny: Demise of the anthophyte hypothesis? Current Biology 10: R106-R109.
Judd, W. S., C. S. Campbell, E. A. Kellogg, P. S. Stevens. 1999. Plant Systematics: a phylogenetic approach. Sinauer Associates, Inc. Sunderland, MA U.S.A.
landry, G. P. 1993. Zamiaceae. Pp. 347-349. InFlora of North America North of Mexico Vol. 2: Pteridophytes and Gymnosperms, eds. Flora of North America Editorial Committee. Oxford University Press, New York, NY.
www.swazi.com/people/cycad/cycadhome.html
www.perth.uwlax.edu/Biology/
www.wisc.edu/botit/img/bot/401/Cycadophyta/
www.life.umd.edu/CBMG/plantbiology.html
www.nd.edu/~fboze/cycads.htm
www.abc.net.au/science/news/stories/s26489.htm

Pictures


circinate vernation in Cycasleaflets	seeds/ovules


seeds/ovules	Boweniasp.

For questions or feedback, contact: Warren Hauk