Gymnosperm.html |
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| Gymnosperms Fossil range: 370–0 Ma Devonian - Recent |
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 White Spruce leaves (needles)
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| Scientific classification | ||
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| Divisions | ||
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Pinophyta (or Coniferophyta) - Conifers |
Gymnosperm (Gymnospermae) are a group of spermatophyte seed-bearing plants with ovules on the edge or blade of an open sporophyll, which are usually arranged in cone-like structures. The other major group of seed-bearing plants, the angiosperms, have ovules enclosed in a carpel, a sporophyll with fused margins. The term gymnosperm comes from the Greek word gumnospermos (γυμνόσπερμος), meaning "naked seeds" and referring to the unenclosed condition of the seeds, as when they are produced they are found naked on the scales of a cone or similar structure. There are between 700 and 900 species of Gymnosperm. Often they are used for many economical uses and as folk medicines. Some common uses for them are soap, varnish, lumber, paint, edible plants, and perfumes.
Gymnosperms are heterosporous, producing microspores that develop into pollen grains and megaspores that are retained in an ovule. After fertilization (joining of the micro- and megaspore), the resulting embryo, along with other cells comprising the ovule, develops into a seed. The seed is a sporophyte resting stage. Reproduction in gymnosperms varies greatly. Cycads and Ginkgo have motile sperm that swim directly to the egg inside the ovule, while conifers and gnetophytes have sperm with no flagella that are conveyed to the egg along a pollen tube which grows through ovule tissue.
Classification
- Further information: Spermatophyte
In early classification schemes, the gymnosperms (Gymnospermae) "naked seed" plants were regarded as a "natural" group. There is conflicting evidence on the question of whether the living gymnosperms form a monophyletic group or whether angiosperms evolved from gymnosperms.1 Numerous fossil gymnosperm clades once existed that are morphologically at least as distinctive as the four living gymnosperm groups, such as Bennettitales, Caytonia and the glossopterids. When these groups are considered, the question of gymnosperm and angiosperm relationships becomes even more complicated.
References
- ^ 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: 1437–1445. doi:, http://www.amjbot.org/cgi/content/full/91/10/1437.
- Burleigh, J. G., and S. Mathews. 2004. Phylogenetic signal in nucleotide data from seed plants: implications for resolving the seed plant tree of life. American Journal of Botany 91: 1599-1613 (abstract)
- Gifford, Ernest M., Adriance S. Foster. 1989. Morphology and Evolution of Vascular Plants. Third edition. WH Freeman and Company, New York.
- Hilton, Jason, and Richard M. Bateman. 2006. Pteridosperms are the backbone of seed-plant phylogeny. Journal of the Torrey Botanical Society 133: 119-168 (abstract)
External links
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