DESCRIPTION OF THE PHYLUM CYCADEOIDOPHYTA (BOLD ET AL. 1987)
| EUKARYA> ARCHAEPLASTIDA> VIRIDIPLANTAE> STREPTOBIONTA> EMBRYOPHYTA> TRACHEOPHYTA> SPERMOPHYTA> CYCADEOIDOPHYTA |
CYCADEOIDOPHYTA LINKS
| 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 1 and 2). However, the strobili (text with tooltip) A strobilus is an axis of fertile appendages. A simple strobilus is an axis of sporophylls. A compound strobilus is an axis of simple fertile axes. Sometimes the compound cones have simple fertile axes that are reduced to a single sporophyll and appear to be simple strobili. of monoecious species are very complex and include both ovulate and staminate sporophylls in a flower-like arrangement (Figure 3). The outer sporophylls bore pollen (text with tooltip) The collective mass of grains produced within the anthers of flowering plants or the male cones of a gymnosperm. In all seed plants, pollen is generated by the development of a microspore into a microgametophyte. The germination of the pollen grain leads to the development of a pollen tube, which delivers two sperm or sperm nuclei to the egg in the ovule. In flowering plants, mature microgametophyte has only two cells, a tube cell and a generative cell. sacs (microsporangia), and the inner sporophylls bore ovules (text with tooltip) An ovule is a structure that contains the megagametophyte in seed plants. The megagametophyte remains within the megasporangium (the nucellus), which is surrounded by layers of integuments. After fertilization, the ovule develops into a seed. which developed with linear tetrads of megaspores. All sporangia were adaxial (text with tooltip) This is derived from two Latin roots that mean toward (ad) the axil (axis). Adaxial is an adjective most often used to describe the leaf surface that is on top or that surface which faces the apical meristem. . Further details of their life histories are not known. |
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| FIGURE 1. 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. Image from Delevoryas (1971) | FIGURE 2. A reconstruction of Williamsonia next to a line drawing of Cycadeoidea. Image from http://www.ucmp.berkeley.edu/IB181/VPL/Cup/Cup4.html | FIGURE 3. A longitudinal section through a bisporangiate strobilus of Cycadedoidea. The ovules were subtended by bracts in a structure that resembled a flower. Image from Sedgewick Museum, Creative Commons |
| SYSTEMATICS OF THE CYCADEOIDOPHYTA Because of the similarities between a flower and the bisexual strobili of the cycadeoids, Tudge (2000) and Crane (1996, Tree of Life Project), Doyle (2006), Hilton and Bateman (2006), and Tomescu (2008) indicate them as sisters to the gnetophytes and flowering plants. Pearson (1995) suggests a relationship between the cycadeoids and the gnetophytes, but includes them in a line separate from the flowering plants. Doyle (2006) and Hilton and Bateman (2006) show them as sisters to the Angiospermophyta in a clade called the Anthophyta. We have separated the gnetophytes from the anthophyte clade as is indicated by almost all molecular studies (e.g. Chaw et al. 2000, Soltis et al. 2002, Matthews 2009, Zhong et al. 2010, Zhong et al. 2011, Ran et al. 2010, Rai et al. 2008). 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. |
 | FIGURE 4. The relationships between spermophytes (seed plants) are an integration of molecular studies (Chaw et al. 2000, Soltis et al. 2002, Matthews 2009, Zhong et al. 2010, Zhong et al. 2011, Ran et al. 2010, Rai et al. 2008), anatomy and fossil evidence (Doyle 2006, Hilton and Bateman 2006, and Tomescu 2008). In this cladogram, the cycadeoids (taxa in shaded box) are sisters to the Caytoniopsida and associated with the flowering plants. |
| LITERATURE CITED Banks, H. P. 1975. Reclassification of Psilophyta. Taxon. 24: 401-413. 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. Cantino, P., J. A. Doyle, S. W. Graham, W. S. Judd, R. G. Olmstead, D. E. Soltis, P. S. Soltis, and M. J. Donoghue. 2007. Towards a phylogenetic nomenclature of Tracheophyta. Taxon 56(3): E1-E44. Chaw S.-M., C. L. Parkinson, Y. Cheng, T. M. Vincent, and J. D. Palmer. 2000. Seed plant phylogeny inferred from all three plant genomes: Monophyly of extant gymnosperms and origin of Gnetales from Conifers. Proceedings of the National Academy of Sciences (USA) 97:4086-4086. 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/ Dittmer, H. J. 1964. Phylogeny and Form in the Plant Kingdom. Van Norstrand Company, Inc. New York. Doyle, J. A. 1998b. Phylogeny of vascular plants. Annual Review of Ecology and Systematics. 29:567-599. Doyle, J. A. 2006. Seed ferns and the origin of angiosperms. Journal of the Torrey Botanical Society. 133(1): 169-209. [C] Kenrick, P. and P. R. Crane. 1997b. The Origin and Early Diversification of Land Plants: A Cladistic Study. Smithsonian Institute Press. Washington, D.C. Nagalingum, N. S., C. R. Marshall, T. B. Quental, H. S. Rai, D. P. Little, and S. Matthews. 2011. Recent synchronous radiation of a living fossil. Science. 334(6057): 795-799. Northington, D. K. and J. R. Goodin. 1984. The Botanical World. Times Mirror/Mosby College Publishing, St. Louis. Pearson, L. C. 1995. The Diversity and Evolution of Plants. CRC Press. New York. Rai, H. S., P. A. Reeves, R. Peakall, R. G. Olmstead, and S. W. Graham. 2008. Inference of higher-order conifer relationships from multi-locus plastid data set. Botany. 86:658-669. Ran, J-H., H. Gao, X-Q. Wang. 2010. Fast evolution of the retroprocessed mitochondrial rps3 gene in Conifer II and further evidence for the phylogeny of gymnosperms. Molecular Phylogenetics and Evolution. 54: 136-149. Soltis, D. E., P. S. Soltis, and M. J. Zanis. 2002. Phylogeny of seed plants based on evidence from eight genes. American Journal of Botany. 89:1670-1681. Soltis, D. E., P. S. Soltis, and M. J. Zanis. 2002. Phylogeny of seed plants based on evidence from eight genes. American Journal of Botany. 89:1670-1681. Tomescu, A. M. F. 2008. Megaphylls, microphylls and the evolution of leaf development. Trends in Plant Science. 14(1): 5-12 Zgurski, J. M., H. S. Rai, Q. M. Fai, D. J. Bogler, and J. Francisco-Ortega. 2008. How well do we understand the overall backbone of cycad phylogeny? New insights from a large, multigene plastid data set. Molecular Phylogenetics and Evolution. 47: 1232-1237. Zhong, B., T. Yonezawa, Y. Zhong, and M. Hasegawa. 2010. The position of Gnetales among seed plants: overcoming pitfalls of chloroplast phylogenomics. Molecular Biology and Evolution. 27(12): 2855-2863. Zhong, B., O. Deusch, V. V. Goremykin, D. Penny, P. J. Biggs, R. A. Atherton, S. V. Nikiforova, and P. J. Lockhart. 2011. Systematic error in seed plant phylogenomics. Genome Biology and Evolution. 3: 1340-1348. |
| By Jack R. Holt. Last revised: 04/08/2013 |
