|TAXA OF LIFE|
Cycadeoidophyta (si-ka-doi-DA-fa-ta) is formed from three Greek roots that mean palm (khoix -χοιζ); like (idio -ίδιο); and plant (phyto -φυτο). The reference is to a plant like a cycad (See the derivation of the Cycadophyta).
INTRODUCTION TO THE CYCADEOIDOPHYTA
The cycadeoids are all extinct, but resemble the cycads in their growth habit and morphology (Figures A&B). However, the strobili of monoecious species are very complex and include both ovulate and staminate sporophylls in a flower-like arrangement. The outer sporophylls bore pollen sacs (microsporangia), and the inner sporophylls bore ovules which developed with linear tetrads of megaspores. All sporangia were adaxial. Further details of their life histories are not known.
SYSTEMATICS OF THE CYCADEOIDOPHYTA
Because of the similarities between a flower and the bisexual strobili of the cycadeoids, Tudge (2000) and the Crane (1996; Tree of Life Project) indicate them as sisters to the gnetophytes and flowering plants. Pearson (1995) indicates a relationship between the cycadeoids and the gnetophytes, but includes them in a line separate from the flowering plants. Doyle (2006) shows them as sisters to the Angiospermophyta. They have a fossil history that extends from the Permian through the Cretaceous, so they overlapped with both groups. In fact, the cycadeoids exhibited high abundance and diversity throughout the Mesozoic.
A. A reconstruction of Cycadeoidea which had a barrel-shaped stem and frond-like leaves, just like the common cycads. However, it had a compound, bisexual strobilus.
B. A reconstruction of Williamsonia next to a line drawing of Cycadeoidea.
|Images taken from:
A: Delevoryas (1971)
SYNOPTIC DESCRIPTION OF THE CYCADEOIDOPHYTA
|The following description comes from Bold et al. (1987) and Bierhorst (1971).|
I. SYNONYMS: cycadeoids, Bennettiales
II. NUMBER: all are extinct
III. PHYLUM CHARACTERISTICS
HIERARCHICAL CLASSIFICATION OF THE CYCADEOIDOPHYTA
|The following system follows Bold et al. (1987) and Bierhorst (1971).|
Bierhorst, D. W. 1971. Morphology of Vascular Plants. In: N. H. Giles and J. G. Torrey. The MacMillan Biology Series. The MacMillan Co. New York.
Bold, H. C., C. J. Alexopoulos, and T. Delevoryas. 1987. Morphology of Plants and Fungi. 5th Edition. HarperCollins Publishers, Inc. New York.
Crane, P.. 1996. Spermatopsida. Seed Plants. Version 01 January 1996 (temporary). http://tolweb.org/Spermatopsida/20622/1996.01.01 in The Tree of Life Web Project, http://tolweb.org/
Doyle, J. A. 2006. Seed ferns and the origin of angiosperms. Journal of the Torrey Botanical Society 133(1): 169-209.
Pearson, L. C. 1995. The Diversity and Evolution of Plants. CRC Press. New York.
Tudge, C. 2000. The Variety of Life, A Survey and a Celebration of all the Creatures That Have Ever Lived. Oxford University Press. New York.
By Jack R. Holt. Last revised: 03/21/2010