Raffi at 04:58, 4 April 2007

2007-04-04T04:58:05Z

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{{Taxobox
| color = lightgreen
| name = Gymnospermae
| image = Fichtennadel.jpg
| image_width = 220px
| image_caption = [[White Spruce]] leaves (needles)
| regnum = [[Plant]]ae
| subdivision_ranks = [[Division (biology)|Divisions]]
| subdivision =
[[Pinophyta]] - Conifers<br>
[[Ginkgo|Ginkgophyta]] - ''Ginkgo''<br>
[[Cycad|Cycadophyta]] - Cycads<br>
[[Gnetophyta]] - ''Gnetum, Ephedra, Welwitschia''
}}

'''Gymnosperms''' (Gymnospermae) are a group of [[seed]]-bearing plants with [[ovule]]s on the edge or blade of an open [[sporophyll]], the sporophylls 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 language|Greek]] word ''gumnospermos'', 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 [[Conifer cone|cone]] or similar structure.

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.

[[Image:Pseudotsuga menziesii cone.jpg|left|thumb|[[Coast Douglas-fir]] cone]]
In early classification schemes, the gymnosperms (Gymnospermae) "naked seed" plants were regarded as a "natural" group. However, certain fossil discoveries suggest that the angiosperms evolved from a gymnosperm ancestor, which would make the gymnosperms a [[paraphyletic]] group if all extinct taxa are included. Modern [[cladistic]]s only accepts taxa that are [[monophyletic]], traceable to a common ancestor and inclusive of all descendants of that common ancestor. So, while the term gymnosperm is still widely used for non-angiosperm seed-bearing plants, the plant species once treated as gymnosperms are usually distributed among four groups, which can be given equal rank as divisions within the [[plant|Kingdom Plantae]].

With regard to extant gymnosperms, molecular phylogenies of living taxa have conflicted with morphological datasets with regard to whether they comprise a monophyletic or paraphyletic group with respect to angiosperms. At issue is whether the Gnetophyta are the sister taxon to angiosperms, or whether they are sister to, or nested within, other extant gymnosperms.

== References ==
*Bowe, L. Michelle, Gwénaële Coat, and Claude W. dePamphilis. 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: 4092-4097 ([http://www.pnas.org/cgi/content/abstract/97/8/4092 abstract]).
*Soltis, Douglas E., Pamela S. Soltis and Michael J. Zanis. 2002. Phylogeny of seed plants based on evidence from eight genes. ''American Journal of Botany'' 89: 1670-1681 ([http://intl.amjbot.org/cgi/content/full/89/10/1670 abstract]).
*Chaw, Shu-Miaw, Christopher L. Parkinson, Yuchang Cheng, Thomas M. Vincent, and Jeffrey 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'' 97: 4086-4091 ([http://www.pnas.org/cgi/content/abstract/97/8/4086 abstract]).

== External links ==
*[http://www.conifers.org/ Gymnosperm Database]

[[Category:Gymnosperms]]
[[Category:Plant taxonomy| sort31 Gymnospermae]]

Gymnosperm - Revision history

Raffi at 04:58, 4 April 2007