TAXA OF LIFE

PHYLUM CYCADEOIDOPHYTA+

EUKARYA>ARCHAEPLASTIDA>VIRIDIPLANTAE>STREPTOBIONTA>EMBRYOPHYTA>TRACHEOPHYTA>SPERMOPHYTA>CYCADEOIDOPHYTA

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.

cycadeoidea-Delevoryas.jpg (99618 bytes)

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.

Williamsonia-Berkeley.gif (13448 bytes)

B. A reconstruction of Williamsonia next to a line drawing of Cycadeoidea.

Images taken from:
A: Delevoryas (1971)
B: http://www.ucmp.berkeley.edu/IB181/VPL/Cup/Cup4.html

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

A. Structure

Habit: The cycadeoids are cycad-like seed plants with barrel-shaped stems and large frond-like leaves. All plants are extinct.

Pollen: Pollen grains are similar to those of the Cycads.

Microstrobilus: Microsporophylls are often fused at the base; technically a simple strobilus which bore both ovulate and pollen-bearing structures.

Seeds: Appear to be similar to those of Cycads.

Megastrobilus: In bisporangiate cones, ovules occur on a central receptacle; the structure suggests either a high degree of self-pollination or a high degree of animal-assisted pollination.

Stems: Very similar to those of the Cycads.

Leaves: Large and frond-like.

Roots: I do not know.

C. Ecology: All plants are extinct. Their fossil history dates from the late Permian to the Cretaceous. They were very abundant during the Mesozoic.

HIERARCHICAL CLASSIFICATION OF THE CYCADEOIDOPHYTA

The following system follows Bold et al. (1987) and Bierhorst (1971).

CLASS CYCADEOIDOPSIDA+.

ORDER CYCADEOIDALES

These plants have a fossil history which ranges from the Permian to the Cretaceous. They are very cycad-like in their growth habit and stem structure. The leaf traces are numerous and c-shaped.

Cycadeoidea.

ORDER WILLIAMSONIALES

These plants have a fossil history which ranges from the early to mid Mesozoic (mainly in the Jurassic). They are tree-like. Many have unisexual cones.

Williamsonia

LITERATURE CITED

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