AskDefine | Define gymnosperm

Dictionary Definition

gymnosperm n : plants of the class Gymnospermae having seeds not enclosed in an ovary

User Contributed Dictionary

English

Pronunciation

Noun

  1. Any plant such as a conifer whose seeds are not enclosed in an ovary.

Adjective

  1. Pertaining to the gymnosperms

Extensive Definition

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, 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.
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 cladistics 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 Kingdom Plantae.
Molecular phylogenies of extant gymnosperms have conflicted with morphological datasets with regard to whether they comprise a monophyletic group or a paraphyletic one that gave rise to angiosperms. At issue is whether the Gnetophyta are the sister group of angiosperms, or whether they are sister to, or nested within, other extant gymnosperms. 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

  • 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

gymnosperm in Arabic: عاريات البذور
gymnosperm in Catalan: Gimnosperma
gymnosperm in Czech: Nahosemenné
gymnosperm in Danish: Nøgenfrøede
gymnosperm in German: Nacktsamige Pflanzen
gymnosperm in Modern Greek (1453-): Γυμνόσπερμο
gymnosperm in Spanish: Gymnospermae
gymnosperm in Esperanto: Gimnospermoj
gymnosperm in Persian: بازدانگان
gymnosperm in French: Gymnospermes
gymnosperm in Korean: 겉씨식물
gymnosperm in Indonesian: Tumbuhan berbiji terbuka
gymnosperm in Italian: Gymnospermae
gymnosperm in Hebrew: חשופי זרע
gymnosperm in Hungarian: Nyitvatermők
gymnosperm in Macedonian: Голосеменици
gymnosperm in Dutch: Naaktzadigen
gymnosperm in Japanese: 裸子植物
gymnosperm in Norwegian: Nakenfrøede planter
gymnosperm in Polish: Nagonasienne
gymnosperm in Portuguese: Gymnospermas
gymnosperm in Quechua: Llat'an muruyuq
gymnosperm in Russian: Голосеменные
gymnosperm in Simple English: Gymnosperm
gymnosperm in Slovenian: Golosemenke
gymnosperm in Swedish: Nakenfröiga växter
gymnosperm in Tamil: வித்துமூடியிலி
gymnosperm in Vietnamese: Thực vật hạt trần
gymnosperm in Turkish: Açık tohumlular
gymnosperm in Ukrainian: Голонасінні
gymnosperm in Chinese: 裸子植物
gymnosperm in Slovak: Nahosemenné rastliny
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