Spermatophyte

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Seed Plants
Temporal range: Devonian? or earlier to recent
Welwitschia mirabilis a member of the Gnetophyta
Scientific classification
Kingdom: Plantae
Subkingdom: Embryophyta
(unranked): Spermatophyta
Divisions
Synonyms
  • Phanerogamae

The spermatophytes (from the Greek word "Σπερματόφυτα") (also known as phanerogams or phenogamae) comprise those plants that produce seeds, hence the alternate name Seed plants. They are a subset of the embryophytes or land plants.

Description

The living spermatophytes form five groups:

In addition to the taxa listed above, the fossil record contains evidence of many extinct taxa of seed plants. The so-called "seed ferns" (Pteridospermae) were one of the earliest successful groups of land plants, and forests dominated by seed ferns were prevalent in the late Paleozoic. Glossopteris was the most prominent tree genus in the ancient southern supercontinent of Gondwana during the Permian period. By the Triassic period, seed ferns had declined in ecological importance, and representatives of modern gymnosperm groups were abundant and dominant through the end of the Cretaceous, when angiosperms radiated. Another Late Paleozoic group of probable spermatophytes were the gigantopterids.

Evolution

A whole genome duplication event in the ancestor of seed plants occurred about 319 million years ago.1 This gave rise to a series of evolutionary changes that resulted in the origin of seed plants.

A middle Devonian precursor to seed plants from Belgium has been identified predating the earliest seed plants by about 20 million years. Runcaria, small and radially symmetrical, is an integumented megasporangium surrounded by a cupule. The megasporangium bears an unopened distal extension protruding above the mutlilobed integument. It is suspected that the extension was involved in anemophilous pollination. Runcaria sheds new light on the sequence of character acquisition leading to the seed. Runcaria has all of the qualities of seed plants except for a solid seed coat and a system to guide the pollen to the seed.2

Relationships and nomenclature

Seed-bearing plants were traditionally divided into angiosperms, or flowering plants, and gymnosperms, which includes the gnetophytes, cycads, ginkgo, and conifers. Older morphological studies believed in a close relationship between the gnetophytes and the angiosperms,3 in particular based on vessel elements. However, molecular studies (and some more recent morphological4 and fossil5 papers) have generally shown a clade of gymnosperms, with the gnetophytes in or near the conifers. For example, one common proposed set of relationships is known as the gne-pine hypothesis and looks like:678


angiosperms (flowering plants)


gymnosperms

cycads 9



Ginkgo





Pinaceae (the pine family)



gnetophytes




other conifers




However, the relationships between these groups should not be considered settled.310

Other classifications group all the seed plants in a single division, with classes for our five groups:

A more modern classification ranks these groups as separate divisions (sometimes under the Superdivision Spermatophyta):

References

  1. ^ Jiao Y, Wickett NJ, Ayyampalayam S, Chanderbali AS, Landherr L, Ralph PE, Tomsho LP, Hu Y, Liang H, Soltis PS, Soltis DE, Clifton SW, Schlarbaum SE, Schuster SC, Ma H, Leebens-Mack J, Depamphilis CW (2011) Ancestral polyploidy in seed plants and angiosperms. Nature
  2. ^ "Science Magazine". Runcaria, a Middle Devonian Seed Plant Precursor. American Association for the Advancement of Science. 2011. Retrieved March 22, 2011. 
  3. ^ a b Jeffrey D. Palmer, Douglas E. Soltis and Mark W. Chase (2004). "The plant tree of life: an overview and some points of view". American Journal of Botany 91 (10): 1437–1445. doi:10.3732/ajb.91.10.1437. PMID 21652302. 
  4. ^ James A. Doyle (January 2006). "Seed ferns and the origin of angiosperms". The Journal of the Torrey Botanical Society 133 (1): 169–209. doi:10.3159/1095-5674(2006)133[169:SFATOO]2.0.CO;2. ISSN 1095-5674. 
  5. ^ Zi-Qiang Wang (2004). "A New Permian Gnetalean Cone as Fossil Evidence for Supporting Current Molecular Phylogeny". Annals of Botany 94 (2): 281–288. doi:10.1093/aob/mch138. PMID 15229124. 
  6. ^ Chaw, Shu-Miaw; Parkinson, Christopher L.; Cheng, Yuchang; Vincent, Thomas M.; Palmer, Jeffrey D. (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 97 (8): 4086–4091. doi:10.1073/pnas.97.8.4086. PMC 18157. PMID 10760277. 
  7. ^ Bowe, L. M.; Michelle, L.; Coat, Gwénaële; Claude (2000). "Phylogeny of seed plants based on all three genomic compartments: Extant gymnosperms are monophyletic and Gnetales' closest relatives are conifers". Proceedings of the National Academy of Sciences 97 (8): 4092–4097. doi:10.1073/pnas.97.8.4092. PMC 18159. PMID 10760278. 
  8. ^ Soltis, Douglas E.; Soltis, Pamela S.; Zanis, Michael J. (2002). "Phylogeny of seed plants based on evidence from eight genes". American Journal of Botany 89 (10): 1670–1681. doi:10.3732/ajb.89.10.1670. PMID 21665594. 
  9. ^ Chung-Shien Wu, Ya-Nan Wang, Shu-Mei Liu and Shu-Miaw Chaw (2007). "Chloroplast Genome (cpDNA) of Cycas taitungensis and 56 cp Protein-Coding Genes of Gnetum parvifolium: Insights into cpDNA Evolution and Phylogeny of Extant Seed Plants". Molecular Biology and Evolution 24 (6): 1366–1379. doi:10.1093/molbev/msm059. PMID 17383970. 
  10. ^ Won, Hyosig; Renner, Susanne (August 2006). "Dating Dispersal and Radiation in the Gymnosperm Gnetum (Gnetales)—Clock Calibration When Outgroup Relationships Are Uncertain". Systematic Biology 55 (4): 610–622. doi:10.1080/10635150600812619. PMID 16969937. 







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