Gymnospermae

From Palaeos

Gymnospermae ('naked seeds') include four classes, the cycads, ginkgos, conifers and Gnetales. They are plants that produce ovules on an open sporophyll (usually in a cone) rather than enclosed within a carpel as in angiosperms. This is a plesiomorphic character for seed plants, and traditionally the gymnosperms have been thought to be paraphyletic with regard to the angiosperms (flowering plants) with the Gnetales as sister to angiosperms. However, recent molecular trees unexpectedly recover the Recent gymnosperms as a monophyletic group, as shown below. This has significant implications for our understanding of reproductive evolution in the seed plants. See Friedman and Floyd (2001) for a review of the alternative phylogenies. Notably, double fertilisation (previously believed a uniting character of Gnetales and angiosperms) may be more widespread among seed plants than previously believed, highlighting the potential dangers of extrapolating observations on a few exemplars to cover larger taxa.

We therefore restrict the name "Gymnospermae" to the clade formed by modern taxa ("anything closer to Cycas, Ginkgo, Pinus and Gnetum than to Magnolia"). A number of fossil taxa have been included in the crown seed plants in the past (see Doyle [1998] for a review), such as corystosperms, Bennettitales, Glossopteridales and Caytonia. It is uncertain whether these fossil 'gymnosperms' would fall within a monophyletic clade of modern Gymnospermae. The large gap in the fossil record between the earliest definite crown Gymnospermae (in the Palaeozoic) and the earliest angiosperms (in the early Cretaceous - Sun et al., 2002) suggests that at least some of the fossil 'gymnosperms' might be expected to lie on the angiosperm stem. In particular, Caytonia and the Bennettitales have been nominated by different authors as angiosperm ancestors.

Phylogeny

<==Gymnospermae [Pinophyta]
   |  i. s.: Gigantopteris [Gigantonomiales, Gigantopteridaceae]
   |         Sanmiguelia
   |         Irania [Iraniales]
   |--Cycadopsida [Cycadophyta]
   |    |  i. s.: Anomozamites
   |    |--Lagenostoma [Lagenostomales]
   |    |--Trigonocarpus Brongniart 1828 [Trigonocarpales]
   |    |--Nilssoniaceae [Nilssoniales]
   |    `--+--Semionogyna
   |       `--Cycadales
   `--Coniferophyta
        |  i. s.: Carpentieria frondosa
        |         Dichophyllum
        |         Genoites patagonica
        |         Ginkgophyllum
        |         Polyspermophyllum sergii
        |         Sphenobaiera
        |         Vojnovskyales
        |           |--Vojnovskya [Vojnovskyaceae]
        |           |    `--V. paradoxa
        |           `--Sergeia neuburgii
        |         Barthelia Rothwell & Mapes 2001 [Bartheliaceae]
        |           `--*B. furcata Rothwell & Mapes 2001
        |         Dicranophyllales
        |--Cordaitales [Cordaitanthales]
        |    |--Cordaites robbii [incl. C. borassifolius]
        |    |--Cordaitanthus devonicus
        |    `--Sternbergia
        `--+--Ginkgoopsida
           `--+--Pinopsida
              `--+--+--Gnetales
                 |  `--Piroconites
                 `--Bennettitales
                      |--Weltrichia
                      |--Williamsonia
                      |--Cycadaeoidea
                      |--Sturiella
                      `--Zamites

* Type species of genus indicated

References

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Doyle, J. A. 1998. Phylogeny of vascular plants. Annual Review of Ecology and Systematics 29: 567-599.

Engel, M. S. 2001. A monograph of the Baltic amber bees and evolution of the Apoidea (Hymenoptera). Bulletin of the American Museum of Natural History 259: 1-192.

Friedman, W. E., & S. K. Floyd. 2001. Perspective: The origin of flowering plants and their reproductive biology – a tale of two phylogenies. Evolution 55 (2): 217-231.

Gomez, B. 2002. A new species of Mirovia (Coniferales, Miroviaceae) from the Lower Cretaceous of the Iberian Ranges (Spain). Cretaceous Research 23: 761-773.

Gomez, B., F. Thévenard, M. Fantin & L. Guisberti. 2002. Late Cretaceous plants from the Bonarelli Level of the Venetian Alps, northeastern Italy. Cretaceous Research 23: 671-685.

Heads, M. 2003. Ericaceae in Malesia: Vicariance biogeography, terrane tectonics and ecology. Telopea 10 (1): 311-449.

Lack, H. W., & H. Ohba. 1998. Die Xylothek des Chikusai Kato. Willdenowia 28: 263-276.

Leschen, R. A. B. 2003. Erotylidae (Insecta: Coleoptera: Cucujoidea): Phylogeny and review. Fauna of New Zealand 47: 1-108.

Ohba, H. 1988. The alpine flora of the Nepal Himalayas: An introductory note. In The Himalayan Plants vol. 1 (H. Ohba & S. B. Malla, eds.) The University Museum, University of Tokyo, Bulletin 31: 19-46.

Polunin, I. 1988. Plants and Flowers of Malaysia. Times Editions: Singapore.

Ren, D., & J. Yin. 2003. New ‘osmylid-like’ fossil Neuroptera from the Middle Jurassic of Inner Mongolia, China. Journal of the New York Entomological Society 111 (1): 1-11.

Rothwell, G. W., & G. Mapes. 2001. Barthelia furcata gen. et sp. nov., with a review of Paleozoic coniferophytes and a discussion of coniferophyte systematics. International Journal of Plant Sciences 162 (3): 637-667.

Shute, C. H., & C. J. Cleal. 2002. Ecology and growth habit of Laveineopteris: A gymnosperm from the Late Carboniferous tropical rain forests. Palaeontology 45 (5): 943-972.

Silberman, J. D., A. G. B. Simpson, J. Kulda, I. Cepicka, V. Hampl, P. J. Johnson & A. J. Roger. 2002. Retortamonad flagellates are closely related to diplomonads – implications for the history of mitochondrial function in eukaryote evolution. Molecular Biology and Evolution 19 (5): 777-786.

Sun, G., Q. Ji, D. L. Dilcher, S. Zheng, K. C. Nixon & X. Wang. 2002. Archaefructaceae, a new basal angiosperm family. Science 296: 899-904.

Suzuki, M., & S. Noshiro. 1988. Wood structure of Himalayan plants. In The Himalayan Plants vol. 1 (H. Ohba & S. B. Malla, eds.) The University Museum, University of Tokyo, Bulletin 31: 341-379.

Zherikhin, V. V. 2002a. Insect trace fossils. In History of Insects (A. P. Rasnitsyn & D. L. J. Quicke, eds.) pp. 303-324. Kluwer Academic Publishers: Dordrecht.

Zherikhin, V. V. 2002b. Ecological history of the terrestrial insects. In History of Insects (A. P. Rasnitsyn & D. L. J. Quicke, eds.) pp. 331-388. Kluwer Academic Publishers: Dordrecht.

Zhou, Z., P. M. Barrett & J. Hilton. 2003. An exceptionally preserved Lower Cretaceous ecosystem. Nature 421: 807-814.

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