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The gymnosperms ( ; ) are a group of woody, perennial Seed plant, typically lacking the protective outer covering which surrounds the seeds in flowering plants, that include Pinophyta, , Ginkgo, and gnetophyta, forming the clade Gymnospermae. (2025). 9780143419549, DK Pub.. ISBN 9780143419549 The term gymnosperm comes from the composite word in ( and ), and literally means 'naked seeds'. The name is based on the unenclosed condition of their seeds (called in their unfertilized state). The non-encased condition of their seeds contrasts with the seeds and ovules of flowering plants (angiosperms), which are enclosed within an ovary. Gymnosperm seeds develop either on the surface of scales or Leaf, which are often modified to form Conifer cone, or on their own as in Taxus, Torreya, and Ginkgo.
The life cycle of a gymnosperm involves alternation of generations, with a dominant diploid sporophyte phase, and a reduced haploid gametophyte phase, which is dependent on the sporophytic phase. The term "gymnosperm" is often used in paleobotany to refer to (the paraphyletic group of) all non-angiosperm seed plants. In that case, to specify the modern monophyletic group of gymnosperms, the term Acrogymnospermae is sometimes used.Coniferae, Gnetophyta. "1 Relationships of Angiosperms to Other Seed Plants."
The gymnosperms and angiosperms together constitute the spermatophytes or seed plants. The spermatophytes are subdivided into five divisions, the angiosperms and four divisions of gymnosperms: the Cycadophyta, Ginkgophyta, Gnetophyta, and Pinophyta (also known as Coniferophyta). Newer classification place the gnetophytes among the conifers. Numerous extinct seed plant groups are recognised including those considered pteridosperms/seed ferns, as well other groups like the Bennettitales.
By far the largest group of living gymnosperms are the conifers (pines, cypresses, and relatives), followed by cycads, gnetophytes ( Gnetum, Ephedra and Welwitschia), and Ginkgo biloba (a single living species). About 65% of gymnosperms are Dioecy, but conifers are almost all Monoecy. Some genera have ectomycorrhiza fungal associations with roots ( Pinus), while in some others ( Cycas) small specialised roots called coralloid roots are associated with nitrogen-fixing cyanobacteria.
All gymnosperms are perennial , Unlike in other extant gymnosperms the soft and highly parenchymatous wood in cycads is poorly lignified, and their main structural support comes from an armor of sclerenchymatous leaf bases covering the stem, with the exception of species with underground stems. There are no Herbaceous plant gymnosperms and compared to angiosperms they occupy fewer , but have evolved both parasites ( Parasitaxus), ( Zamia pseudoparasitica) and ( Retrophyllum minus).
are by far the most abundant extant group of gymnosperms with six to eight families, with a total of 65–70 genera and 600–630 species (696 accepted names). Most conifers are .Campbell, Reece, "Phylum Coniferophyta."Biology. 7th. 2005. Print. P.595 The leaf of many conifers are long, thin and needle-like, while other species, including most Cupressaceae and some Podocarpaceae, have flat, triangular scale-like leaves. Agathis in Araucariaceae and Nageia in Podocarpaceae have broad, flat strap-shaped leaves.
, small palm-like trees, are the next most abundant group of gymnosperms, with two or three families, 11 genera, and approximately 338 species. A majority of cycads are native to tropical climates and are most abundantly found in regions near the equator. The other extant groups are the 95–100 species of Gnetophyta and one species of Ginkgo. The ginkgo or maidenhair trees are tall and have bilobed leaves, while gnetophytes are a diverse groups of plants and shrubs including the horizontally growing welwitschia
Today, gymnosperms are the most threatened of all plant groups.
The extant gymnosperms include 12 main families and 83 genera which contain more than 1000 known species.
Subclass Cycadidae
Subclass Ginkgoidae
Subclass Gnetidae
Subclass Pinidae
During pollination, pollen grains are physically transferred between plants from the pollen cone to the ovule. Pollen is usually moved by wind or insects. Whole grains enter each ovule through a microscopic gap in the ovule coat (integument) called the micropyle. The pollen grains mature further inside the ovule and produce sperm cells. Two main modes of fertilization are found in gymnosperms. Cycads and Ginkgo have flagellum motile sperm that swim directly to the egg inside the ovule, whereas conifers and have sperm with no flagella that are moved along a pollen tube to the egg. After Fertilisation (joining of the sperm and egg cell), the zygote develops into an embryo (young sporophyte). More than one embryo is usually initiated in each gymnosperm seed. The mature seed comprises the embryo and the remains of the female gametophyte, which serves as a food supply, and the Seed-coat.
Gymnosperms ordinarily reproduce by sexual reproduction, and only rarely express parthenogenesis.Hörandl E. Apomixis and the paradox of sex in plants. Ann Bot. 2024 Mar 18:mcae044. doi: 10.1093/aob/mcae044. Epub ahead of print. PMID 38497809 Sexual reproduction in gymnosperms appears to be required for maintaining long-term genome integrity. Meiosis in sexual land plants provides a direct mechanism for DNA repair in reproductive tissues. The likely primary benefit of cross-pollination in gymnosperms, as in other eukaryotes, is that it allows the avoidance of inbreeding depression caused by the presence of recessive deleterious mutations.Charlesworth D, Willis JH. The genetics of inbreeding depression. Nat Rev Genet. 2009 Nov;10(11):783-96. doi: 10.1038/nrg2664. PMID 19834483
Genetics
The first published sequenced genome for any gymnosperm was the genome of Picea abies in 2013.
Uses
Gymnosperms have major economic uses. Some, such as pine, fir, spruce, and cedar, are used for lumber, paper production, and resin. Some other common uses for gymnosperms are soap, varnish, nail polish, food, gum, and .
General bibliography
External links
[[Category:Gymnosperms|01]]
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