Gymnosperm

Source: Wikipedia, the free encyclopedia.
Not to be confused with the flowering plant genera Gymnosperma and Gymnospermium.

Gymnosperm
Temporal range: Carboniferous–Present
Various gymnosperms.
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Spermatophytes
Clade: Gymnospermae
Living orders[1]

The gymnosperms (

monophyletic
group of gymnosperms, the term Acrogymnospermae is sometimes used.

The gymnosperms and

Pinophyta (also known as Coniferophyta). Newer classification place the gnetophytes among the conifers.[3] Numerous extinct seed plant groups are recognised including those considered pteridosperms/seed ferns, as well other groups like the Bennettitales.[4]

By far the largest group of living gymnosperms are the conifers (pines, cypresses, and relatives), followed by cycads, gnetophytes (

Ephedra and Welwitschia), and Ginkgo biloba (a single living species). About 65% of gymnosperms are dioecious,[5] but conifers are almost all monoecious.[6]

Some genera have mycorrhiza, fungal associations with roots (Pinus), while in some others (Cycas) small specialised roots called coralloid roots are associated with nitrogen-fixing cyanobacteria.

Diversity and origin

Encephalartos sclavoi cone, about 30 cm long

Over 1,000 living species of gymnosperm exist.

progymnosperms of the late Devonian period around 383 million years ago. It has been suggested that during the mid-Mesozoic era, pollination of some extinct groups of gymnosperms was by extinct species of scorpionflies that had specialized proboscis for feeding on pollination drops. The scorpionflies likely engaged in pollination mutualisms with gymnosperms, long before the similar and independent coevolution of nectar-feeding insects on angiosperms.[10][11] Evidence has also been found that mid-Mesozoic gymnosperms were pollinated by Kalligrammatid lacewings, a now-extinct family with members which (in an example of convergent evolution) resembled the modern butterflies that arose far later.[12]

Zamia integrifolia, a cycad native to Florida

All gymnosperms are perennial woody plants,[13] Unlike in other extant gymnosperms the soft and highly parenchymatous wood in cycads is poorly lignified,[14] and their main structural support comes from an armor of sclerenchymatous leaf bases covering the stem,[15] with the exception of species with underground stems.[16] There are no herbaceous gymnosperms and compared to angiosperms they occupy fewer ecological niches, but have evolved both parasites (Parasitaxus), epiphytes (Zamia pseudoparasitica) and rheophytes (Retrophyllum minus).[17]

Conifers 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).[18] Most conifers are evergreens.[19] The leaves 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.

Cycads 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 Gnetales and one species of Ginkgo.[4]

Today gymnosperms are the most threatened of all plant groups.[20]

Classification

Phylogeny of Gymnosperms[21][22][23][24]
Pinidae
Araucariales
Araucariaceae
Araucarieae

Araucaria

Agathideae
Podocarpaceae
Phyllocladoideae
⊞
⊟
Cupressales
Further information:
Spermatophyte

A formal classification of the living gymnosperms is the "Acrogymnospermae", which form a

glossopterids, and Caytonia
are considered, it is clear that angiosperms are nested within a larger gymnospermae clade, although which group of gymnosperms is their closest relative remains unclear.

The extant gymnosperms include 12 main families and 83 genera which contain more than 1000 known species.[2][26][28]

Subclass Cycadidae

Subclass Ginkgoidae

Subclass

Gnetidae

Subclass Pinidae

Extinct groupings

Life cycle

Example of gymnosperm lifecycle

Gymnosperms, like all

seed plants, they are heterosporous, having two spore types, microspores (male) and megaspores (female) that are typically produced in pollen cones or ovulate cones, respectively.[29] The exception is the females in the cycad genus Cycas, which form a loose structure called megasporophylls instead of cones.[30] As with all heterosporous plants, the gametophytes develop within the spore wall. Pollen grains (microgametophytes) mature from microspores, and ultimately produce sperm cells.[29] Megagametophytes develop from megaspores and are retained within the ovule. Gymnosperms produce multiple archegonia
, which produce the female gamete.

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 (

seed coat.[32]

Gymnosperms ordinarily reproduce by sexual reproduction, and only rarely express parthenogenesis[33]. Sexual reproduction in gymnosperms appears to be required for maintaining long-term genomic integrity [33]. Meiosis in sexual land plants provides a direct mechanism for repairing DNA in reproductive tissues[33]. 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[34].

Genetics

The first published sequenced genome for any gymnosperm was the genome of Picea abies in 2013.[35]

Uses

Gymnosperms have major economic uses. Pine, fir, spruce, and cedar are all examples of conifers that are used for lumber, paper production, and resin. Some other common uses for gymnosperms are soap, varnish, nail polish, food, gum, and perfumes.[36]

References

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  2. ^ a b c "Gymnosperms on The Plant List". Theplantlist.org. Archived from the original on 2013-08-24. Retrieved 2013-07-24.
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  4. ^ a b Raven, P.H. (2013). Biology of Plants. New York: W.H. Freeman and Co.
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  18. ^ A. Farjon, ed. (2006). "Conifer database". Catalogue of Life: 2008 Annual checklist. Archived from the original on January 15, 2009.
  19. ^ Campbell, Reece, "Phylum Coniferophyta."Biology. 7th. 2005. Print. P.595
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  25. ^ Cantino 2007.
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  29. ^ a b Samantha, Fowler; Rebecca, Roush; James, Wise (2013). "14.3 Seed Plants: Gymnosperms". Concepts of Biology. Houston, Texas: OpenStax. Retrieved 31 March 2023.
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  32. ISBN 978-0-7872-2108-9
    . Gymnosperm seeds.
  33. ^ a b c 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
  34. ^ Charlesworth D, Willis JH. The genetics of inbreeding depression. Nat Rev Genet. 2009 Nov;10(11):783-96. doi: 10.1038/nrg2664. PMID: 19834483
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General bibliography

External links

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