DESCRIPTION OF THE PHYLUM GINKGOOPHYTA (BOLD 1956)
| EUKARYA> ARCHAEPLASTIDA> VIRIDIPLANTAE> STREPTOBIONTA> EMBRYOPHYTA> TRACHEOPHYTA> SPERMOPHYTA> GINKGOOPHYTA |
GINKGOOPHYTA LINKS
| Ginkgoophyta (gin-ko-AH-fa-ta) is made of a Japanese and a Greek root that together mean silver apricot (ginkyo) and plant (phyto -φυτό). |
| INTRODUCTION TO THE GINKGOOPHYTA The ginkgophytes are represented by a single extant species. However, like the cycads, they have a fossil history that extends back to the Paleozoic and another radiation during the Mesozoic (Figure 1). Also, the extant species (Ginkgo biloba) is dioecious (text with tooltip) Dioecious organisms have separate male and female individuals. . Vegetatively, however, the ginkgophytes more closely resemble conifers with woody monopodial (text with tooltip) Monopodial (adj.) pseudopodia describes the condition where an amoeboid makes a single major pseudopodium at a time. growth, spur shoots (text with tooltip) A slow growing, highly reduced shoot. , long shoots, and conifer-like roots. Unlike conifers, the fan-like leaves of Ginkgo have fern-like dichotomously branched venation. Leaves of the long shoots have a notch in the middle of the fan to produce a bilobed leaf (thus the Latin name; see Figure 2). The ovules and staminate strobili emerge from the spur shoots (Figures 3&4). The ovules are borne in pairs at the tips of specialized and highly reduced megasporophylls. Like the cycads, the ginkgophytes have multiflagellate sperm. Otherwise, the details of the Ginkgo life history (Figure 5) are similar to those of Pinus [See the Introduction to the Coniferophyta]. |
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| FIGURE 1. A fossil of Dichophyllum, the earliest known ginkgophyte from the Paleozoic. Note the leaves that have multiple lobing. Image from http://taggart.glg.msu.edu/bot335/ginkgo.htm | FIGURE 2. Ginkgo leaves growing from a developing long shoot. Note the notched, bilobed appearance of the fan-shaped leaves. Image from http://www.science.siu.edu/landplants/Ginkgophyta/ginkgophyta.html | FIGURE 3. Ginkgo ovules emerging from a spur shoot. Image from http://www.science.siu.edu/landplants/Ginkgophyta/ginkgophyta.html | FIGURE 4. Ginkgo staminate cones emerging from a spur shoot. Image from http://www.science.siu.edu/landplants/Ginkgophyta/ginkgophyta.html |
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| FIGURE 5. Life cycle of Ginkgo biloba. This species is dioecious: ovulate (A) and staminate (B). two ovules on a common peduncle (C), two mature microsporangia from a staminate strobilus (D). Pollen develops from a microspore (F), in which the microgametophytes germinates (F) and develops (G) in the pollen chamber of the ovule (H). Sperm nuclei are delivered to the archegonia by pollen tubes (G). The embryo (I) develops within a seed that has a fleshy berry-like outer integument (I & J). Dittmer 1964 |
 | FIGURE 6. The relationships between spermophytes (seed plants) is 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, Cantino et al. 2007), anatomy and fossil evidence (Doyle 2006, Hilton and Bateman 2006, and Tomescu 2008). In this cladogram, the ginkgophytes (taxa in shaded box) are monophyletic and are sisters to the conifers + gnetophytes. |
| SYSTEMATICS OF THE GINKGOOPHYTA Crane (1996, Tree of Life Project) illustrates the ginkgophytes as surviving seed ferns. Tudge (2000) shows them as a sister group to both the cycads and the conifers. The molecular evidence of Chaw et al. (2000) suggests a similar relationship. Even Pearson (1995) supports this view. Doyle (2006), Hilton and Bateman (2006), and Tomescu (2008) in their anatomical and fossil analyses of gymnosperms and angiosperms, place the ginkgos as sisters to the conifers or a branch within the conifer clade. Figure 6 is an integration of molecular and fossil trees. Until there is clear consensus, we will treat them as separate phyla. |
| 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. 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] Hilton, J. and R. M. Bateman. 2006. Pteridosperms are the backbone of seed-plant phylogeny. Journal of the Torrey Botanicaal Society. 133(1): 119-168. Kenrick, P. and P. R. Crane. 1997b. The Origin and Early Diversification of Land Plants: A Cladistic Study. Smithsonian Institute Press. Washington, D.C. 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. 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. Zhu, W.-Q. and P. Kenrick. 1999. A Zosterophyllum-like plant from the lower Devonian of Yunnan Province, China. Review of Palaeobotany and Palynology. 105: 111-118. |
| By Jack R. Holt. Last revised: 04/03/2014 |
