Gymnosperm

The gymnosperms, also known as Acrogymnospermae,[1] are a group of seed-producing plants that includes conifers, cycads, Ginkgo, and gnetophytes. The term "gymnosperm" comes from the composite word in Greek: γυμνόσπερμος (γυμνός, gymnos, 'naked' and σπέρμα, sperma, 'seed'), literally meaning "naked seeds". The name is based on the unenclosed condition of their seeds (called ovules 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 leaves, which are often modified to form cones, or solitary as in yew, Torreya, Ginkgo.[2]

The gymnosperms and angiosperms together compose the spermatophytes or seed plants. The gymnosperms are divided into six phyla. Organisms that belong to the Cycadophyta, Ginkgophyta, Gnetophyta, and Pinophyta (also known as Coniferophyta) phyla are still in existence while those in the Pteridospermales and Cordaitales phyla are now extinct.[3]

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).

Roots in some genera have fungal association with roots in the form of mycorrhiza (Pinus), while in some others (Cycas) small specialised roots called coralloid roots are associated with nitrogen-fixing cyanobacteria.

Gymnospermae
Temporal range: Carboniferous - Present
Gymnospermae
Various gymnosperms.
Scientific classification
Kingdom:
Subkingdom:
(unranked):
(unranked):
Gymnospermae (inc. ; paraphyletic)
Acrogymnospermae (extant only)
Divisions

Pinophyta (or Coniferophyta) - Conifers
Ginkgophyta - Ginkgo
Cycadophyta - Cycads
Gnetophyta - Gnetum, Ephedra, Welwitschia

Encephalartos sclavoi reproductive cone
Encephalartos sclavoi cone, about 30 cm long

Classification

The current formal classification of the living gymnosperms is the "Acrogymnospermae", which form a monophyletic group within the spermatophytes.[1][4] The wider "Gymnospermae" group includes extinct gymnosperms and is thought to be paraphyletic. The fossil record of gymnosperms includes many distinctive taxa that do not belong to the four modern groups, including seed-bearing trees that have a somewhat fern-like vegetative morphology (the so-called "seed ferns" or pteridosperms).[5] When fossil gymnosperms such as these and the Bennettitales, 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][4][6]

Subclass Cycadidae

  • Order Cycadales
    • Family Cycadaceae: Cycas
    • Family Zamiaceae: Dioon, Bowenia, Macrozamia, Lepidozamia, Encephalartos, Stangeria, Ceratozamia, Microcycas, Zamia.

Subclass Ginkgoidae

Subclass Gnetidae

Subclass Pinidae

  • Order Pinales
    • Family Pinaceae: Cedrus, Pinus, Cathaya, Picea, Pseudotsuga, Larix, Pseudolarix, Tsuga, Nothotsuga, Keteleeria, Abies
  • Order Araucariales
    • Family Araucariaceae: Araucaria, Wollemia, Agathis
    • Family Podocarpaceae: Phyllocladus, Lepidothamnus, Prumnopitys, Sundacarpus, Halocarpus, Parasitaxus, Lagarostrobos, Manoao, Saxegothaea, Microcachrys, Pherosphaera, Acmopyle, Dacrycarpus, Dacrydium, Falcatifolium, Retrophyllum, Nageia, Afrocarpus, Podocarpus
  • Order Cupressales
    • Family Sciadopityaceae: Sciadopitys
    • Family Cupressaceae: Cunninghamia, Taiwania, Athrotaxis, Metasequoia, Sequoia, Sequoiadendron, Cryptomeria, Glyptostrobus, Taxodium, Papuacedrus, Austrocedrus, Libocedrus, Pilgerodendron, Widdringtonia, Diselma, Fitzroya, Callitris, Actinostrobus, Neocallitropsis, Thujopsis, Thuja, Fokienia, Chamaecyparis, Cupressus, Juniperus, Calocedrus, Tetraclinis, Platycladus, Microbiota
    • Family Taxaceae: Austrotaxus, Pseudotaxus, Taxus, Cephalotaxus, Amentotaxus, Torreya

Diversity and origin

There are over 1000 living species of gymnosperm.[2] It is widely accepted that the gymnosperms originated in the late Carboniferous period, replacing the lycopsid rainforests of the tropical region.[7][8] This appears to have been the result of a whole genome duplication event around 319 million years ago.[9] Early characteristics of seed plants were evident in fossil 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 genus with members which (in an example of convergent evolution) resembled the modern butterflies that arose far later.[12]

Zamia integrifolia02
Zamia integrifolia, a cycad native to Florida

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).[13] Conifers are woody plants and most are evergreens.[14] The leaves of many conifers are long, thin and needle-like, 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.[3]

Spermatophyta

Pteridospermatophyta

Acrogymnospermae

Angiospermae

Gymnospermae

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.

Life cycle

Gymnosperm life cycle (en)
Example of gymnosperm lifecycle

Gymnosperms, like all vascular plants, have a sporophyte-dominant life cycle, which means they spend most of their life cycle with diploid cells, while the gametophyte (gamete-bearing phase) is relatively short-lived. Two spore types, microspores and megaspores, are typically produced in pollen cones or ovulate cones, respectively. Gametophytes, as with all heterosporous plants, develop within the spore wall. Pollen grains (microgametophytes) mature from microspores, and ultimately produce sperm cells. 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 (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 motile sperm that swim directly to the egg inside the ovule, whereas conifers and gnetophytes have sperm with no flagella that are moved along a pollen tube to the egg. After syngamy (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.[15]

Genetics

The first published sequenced genome for any gymnospermae was the genome of Picea abies in 2013.[16]

References

  1. ^ a b D., Cantino, Philip; A., Doyle, James; W., Graham, Sean; S., Judd, Walter; G., Olmstead, Richard; E., Soltis, Douglas; S., Soltis, Pamela; J., Donoghue, Michael. "Towards a phylogenetic nomenclature of Tracheophyta". www.ingentaconnect.com. Retrieved 2018-10-18.
  2. ^ a b c "Gymnosperms on The Plant List". Theplantlist.org. Retrieved 2013-07-24.
  3. ^ a b Raven, P.H. (2013). Biology of Plants. New York: W.H. Freeman and Co.
  4. ^ a b Christenhusz, M.J.M.; Reveal, J.L.; Farjon, A.; Gardner, M.F.; Mill, R.R.; Chase, M.W. (2011). "A new classification and linear sequence of extant gymnosperms" (PDF). Phytotaxa. 19: 55–70. doi:10.11646/phytotaxa.19.1.3.
  5. ^ 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)
  6. ^ Christenhusz, M. J. M.; Byng, J. W. (2016). "The number of known plants species in the world and its annual increase". Phytotaxa. 261 (3): 201–217. doi:10.11646/phytotaxa.261.3.1.
  7. ^ Sahney, S.; Benton, M.J. & Falcon-Lang, H.J. (2010). "Rainforest collapse triggered Pennsylvanian tetrapod diversification in Euramerica" (PDF). Geology. 38 (12): 1079–1082. Bibcode:2010Geo....38.1079S. doi:10.1130/G31182.1.
  8. ^ Campbell and Reece; Biology, Eighth edition
  9. ^ Jiao Y, Wickett NJ, Ayyampalayam S, Chanderbali AS, Landherr L, Ralph PE, Tomsho LP, Hu Y, Liang H, Soltis PS, Soltis DE, Clifton SW, Schlarbaum SE, Schuster SC, Ma H, Leebens-Mack J, Depamphilis CW (2011) Ancestral polyploidy in seed plants and angiosperms. Nature
  10. ^ Ollerton, J.; Coulthard, E. (2009). "Evolution of Animal Pollination". Science. 326 (5954): 808–809. Bibcode:2009Sci...326..808O. doi:10.1126/science.1181154. PMID 19892970.
  11. ^ Ren, D; Labandeira, CC; Santiago-Blay, JA; Rasnitsyn, A; et al. (2009). "A Probable Pollination Mode Before Angiosperms: Eurasian, Long-Proboscid Scorpionflies". Science. 326 (5954): 840–847. Bibcode:2009Sci...326..840R. doi:10.1126/science.1178338. PMC 2944650. PMID 19892981.
  12. ^ Labandeira, Conrad C.; Yang, Qiang; Santiago-Blay, Jorge A.; Hotton, Carol L.; Monteiro, Antónia; Wang, Yong-Jie; Goreva, Yulia; Shih, ChungKun; Siljeström, Sandra; Rose, Tim R.; Dilcher, David L.; Ren, Dong (2016). "The evolutionary convergence of mid-Mesozoic lacewings and Cenozoic butterflies". Proceedings of the Royal Society B: Biological Sciences. 283 (1824): 20152893. doi:10.1098/rspb.2015.2893. PMC 4760178. PMID 26842570.
  13. ^ Catalogue of Life: 2007 Annual checklist - Conifer database Archived January 15, 2009, at the Wayback Machine
  14. ^ Campbell, Reece, "Phylum Coniferophyta."Biology. 7th. 2005. Print. P.595
  15. ^ Walters, Dirk R Walters Bonnie By (1996). Vascular plant taxonomy. Dubuque, Iowa: Kendall/Hunt Pub. Co. p. 124. ISBN 978-0-7872-2108-9.
  16. ^ Nystedt, B; Street, NR; Wetterbom, A; et al. (May 2013). "The Norway spruce genome sequence and conifer genome evolution". Nature. 497 (7451): 579–584. Bibcode:2013Natur.497..579N. doi:10.1038/nature12211. PMID 23698360.

External links

Coniferyl alcohol

Coniferyl alcohol is an organic compound. This colourless crystalline solid is a phytochemical, one of the monolignols. It is synthesized via the phenylpropanoid biochemical pathway. When copolymerized with related aromatic compounds, coniferyl alcohol forms lignin or lignans. Coniferin is a glucoside of coniferyl alcohol.

Coniferyl alcohol is an intermediate in biosynthesis of eugenol and of stilbenoids and coumarin. Gum benzoin contains significant amount of coniferyl alcohol and its esters.

It is found in both gymnosperm and angiosperm plants. Sinapyl alcohol and paracoumaryl alcohol, the other two lignin monomers, are found in angiosperm plants and grasses.

It is a queen retinue pheromone (QRP), a type of honey bee pheromone found in the mandibular glands.

Cycas circinalis

Cycas circinalis, also known as the queen sago, is a species of cycad known in the wild only from southern India. Cycas circinalis is the only gymnosperm species found among native Sri Lankan flora.

Ephedra (plant)

Ephedra is a genus of gymnosperm shrubs, the only genus in its family, Ephedraceae, and order, Ephedrales. The various species of Ephedra are widespread in many lands, native to southwestern North America, southern Europe, northern Africa, southwest and central Asia, northern China and western South America.In temperate climates, most Ephedra species grow on shores or in sandy soils with direct sun exposure. Common names in English include joint-pine, jointfir, Mormon-tea or Brigham tea. The Chinese name for Ephedra species is mahuang (simplified Chinese: 麻黄; traditional Chinese: 麻黃; pinyin: máhuáng; Wade–Giles: ma-huang; literally: 'hemp yellow'). Ephedra is also sometimes called sea grape (from the French raisin de mer), a common name for the flowering plant Coccoloba uvifera.

Eucommiidites

Eucommiidites is an angiosperm look-alike pollen type from the Mesozoic Era. When it was first described in Sweden, it was thought to represent pollen from the earliest angiosperms. However, it was subsequently shown, due to morphology, that it could not be angiospermous. Later, Eucommidites pollen was discovered in the pollen chambers of fossil gymnosperm seeds.

Eucommidites is tricolpate, which is why it was originally thought to be angiospermous. However, the three colpi are not equal in length, and the exine of the pollen grain is similar to a gymnosperm.

Eucommidites is important in biostratigraphy, and it ranges from the Triassic to the Cretaceous.

Ginkgo

Ginkgo is a genus of highly unusual non-flowering plants. The scientific name is also used as the English name. The order to which it belongs, Ginkgoales, first appeared in the Permian, 270 million years ago, possibly derived from "seed ferns" of the order Peltaspermales, and now only contains this single genus and species. The rate of evolution within the genus has been slow, and almost all its species had become extinct by the end of the Pliocene; the exception is the sole living species, Ginkgo biloba, which is only found in the wild in China, but is cultivated across the world. The relationships between ginkgos and other groups of plants are not fully resolved.

Ginkgoales

Ginkgoales or Ginkgophyte is a gymnosperm order containing only one extant species: Ginkgo biloba, the ginkgo tree. It is monotypic, (the only taxon) within the class Ginkgoopsida, which itself is monotypic within the division Ginkgophyta. The order includes five families, of which only Ginkgoaceae remains extant.

Gnetophyta

Gnetophyta is a division of plants, grouped within the gymnosperms (which also includes conifers, cycads, and ginkgos), that consists of some 70 species across the three relict genera: Gnetum (family Gnetaceae), Welwitschia (family Welwitschiaceae), and Ephedra (family Ephedraceae). Fossilized pollen attributed to a close relative of Ephedra has been dated as far back as the Early Cretaceous. Though diverse and dominant in the Paleogene and the Neogene, only three families, each containing a single genus, are still alive today. The primary difference between gnetophytes and other gymnosperms is the presence of vessel elements, a system of conduits that transport water within the plant, similar to those found in flowering plants. Because of this, gnetophytes were once thought to be the closest gymnosperm relatives to flowering plants, but more recent molecular studies have brought this hypothesis into question.

Though it is clear they are all closely related, the exact evolutionary inter-relationships between gnetophytes are unclear. Some classifications hold that all three genera should be placed in a single order (Gnetales), while other classifications say they should be distributed among three separate orders, each containing a single family and genus. Most morphological and molecular studies confirm that the genera Gnetum and Welwitschia diverged from each other more recently than they did from Ephedra.

Gnetum

Gnetum is a genus of gymnosperms, the sole genus in the family Gnetaceae and order Gnetales. They are tropical evergreen trees, shrubs and lianas. Unlike other gymnosperms, they possess vessel elements in the xylem. Some species have been proposed to have been the first plants to be insect-pollinated as their fossils occur in association with extinct pollinating scorpionflies. Molecular phylogenies based on nuclear and plastid sequences from most of the species indicate hybridization among some of the Southeast Asian species. Fossil-calibrated molecular-clocks suggest that the Gnetum lineages now found in Africa, South America and Southeast Asia are the result of ancient long-distance dispersal across seawater.

Haldina

Haldina cordifolia, syn. Adina cordifolia, is a flowering plant in the family Rubiaceae, the sole species in the genus Haldina. It is native to southern Asia, from India east to Yunnan and Vietnam and south to Peninsular Malaysia. It is known as Kadam or Kadamba in Hindi and Gáo trò in Vietnamese.

Haldina cordifolia is a deciduous tree that can grow well over 20 metres high. The flowers may be insignificant individually but can be seen as attractive when they bloom together in inflorescences with a circumference of 20–30 mm. They are usually yellow often tinged with a shade of pink. H. cordifolia usually blossoms during winter (dry season) months. The bark of the tree acts as an antiseptic.

Hardwood

Hardwood is wood from dicot trees. These are usually found in broad-leaved temperate and tropical forests. In temperate and boreal latitudes they are mostly deciduous, but in tropics and subtropics mostly evergreen. Hardwood contrasts with softwood (which is from gymnosperm trees).

List of culinary nuts

A culinary nut is a dry, edible fruit or seed that usually, but not always, has a high fat content. Nuts are used in a wide variety of edible roles, including in baking, as snacks (either roasted or raw), and as flavoring. In addition to botanical nuts, fruits and seeds that have a similar appearance and culinary role are considered to be culinary nuts. Culinary nuts are divided into fruits or seeds in one of four categories:

True, or botanical nuts: dry, hard-shelled, uncompartmented fruit that do not split on maturity to release seeds;

Drupes: seed contained within a pit (stone or pyrene) that itself is surrounded by a fleshy fruit (e.g. almonds);

Gymnosperm seeds: naked seeds, with no enclosure (e.g. pine nuts);

Angiosperm: seeds surrounded by an enclosure, such as a pod or a fruit (e.g. peanuts).Nuts have a rich history as food. For many indigenous peoples of the Americas, a wide variety of nuts, including acorns, American beech, and others, served as a major source of starch and fat over thousands of years. Similarly, a wide variety of nuts have served as food for Indigenous Australians for many centuries. Other culinary nuts, though known from ancient times, have seen dramatic increases in use in modern times. The most striking such example is the peanut. Its usage was popularized by the work of George Washington Carver, who discovered and popularized many applications of the peanut after employing peanut plants for soil amelioration in fields used to grow cotton.

List of edible seeds

An edible seed is a seed that is suitable for human or animal consumption. Of the six major plant parts, seeds are the dominant source of human calories and protein. A wide variety of plant species provide edible seeds; most are angiosperms, while a few are gymnosperms. As a global food source, the most important edible seeds by weight are cereals, followed by legumes, nuts. and then spices.

Cereals and legumes correspond with the botanical families Poaceae and Fabaceae, respectively, while nuts, pseudocereals, and other seeds form polyphylic groups based on their culinary roles.

List of superlative trees

The world's superlative trees can be ranked by any factor. Records have been kept for trees with superlative height, trunk diameter or girth, canopy coverage, airspace volume, wood volume, estimated mass, and age.

Picea abies

Picea abies, the Norway spruce or European spruce, is a species of spruce native to Northern, Central and Eastern Europe. It has branchlets that typically hang downwards, and the largest cones of any spruce, 9–17 cm (3 1⁄2–6 3⁄4 in) long. It is very closely related to the Siberian spruce (Picea obovata), which replaces it east of the Ural Mountains, and with which it hybridises freely. The Norway spruce is widely planted for its wood, and is the species used as the main Christmas tree in several cities around the world. It was the first gymnosperm to have its genome sequenced, and one clone has been measured as 9,560 years old.

The Latin specific epithet abies means “fir-like”.

Plant stem

A stem is one of two main structural axes of a vascular plant, the other being the root. The stem is normally divided into nodes and internodes:

The nodes hold one or more leaves, as well as buds which can grow into branches (with leaves, conifer cones, or inflorescences (flowers)). Adventitious roots may also be produced from the nodes.

The internodes distance one node from another.The term "shoots" is often confused with "stems"; "shoots" generally refers to new fresh plant growth including both stems and other structures like leaves or flowers. In most plants stems are located above the soil surface but some plants have underground stems.

Stems have four main functions which are:

Support for and the elevation of leaves, flowers and fruits. The stems keep the leaves in the light and provide a place for the plant to keep its flowers and fruits.

Transport of fluids between the roots and the shoots in the xylem and phloem(see below)

Storage of nutrients

Production of new living tissue. The normal lifespan of plant cells is one to three years. Stems have cells called meristems that annually generate new living tissue.Stems have two pipe-like tissues called xylem and phloem. The xylem tissue transports water by the action of transpiration pull, capillary action and root pressure. The phloem tissue consists of sieve tubes and their companion cells. The two tissues are separated by cambium which is a tissue that divides to form xylem or phloem cells.

Podocarpaceae

Podocarpaceae is a large family of mainly Southern Hemisphere conifers, comprising about 156 species of evergreen trees and shrubs. It contains 19 genera if Phyllocladus is included and if Manoao and Sundacarpus are recognized.

The family is a classic member of the Antarctic flora, with its main centres of diversity in Australasia, particularly New Caledonia, Tasmania, and New Zealand, and to a slightly lesser extent Malesia and South America (primarily in the Andes mountains). Several genera extend north of the equator into Indochina and the Philippines. Podocarpus reaches as far north as southern Japan and southern China in Asia, and Mexico in the Americas, and Nageia into southern China and southern India. Two genera also occur in sub-Saharan Africa, the widespread Podocarpus and the endemic Afrocarpus.

Parasitaxus usta is unique as the only known parasitic gymnosperm. It occurs on New Caledonia, where it is parasitic on another member of the Podocarpaceae, Falcatifolium taxoides.The genus Phyllocladus is sister to Podocarpaceae sensu stricto. It is treated by some botanists in its own family Phyllocladaceae.

Softwood

Softwood is wood from gymnosperm trees such as conifers, as well as Amborella. The term is opposed to hardwood, which is the wood from angiosperm trees.

Sphenobaiera

Sphenobaiera is a form genus for plant leaves found in rocks from Triassic to Cretaceous periods. The genus Sphenobaiera is used for plants with wedge-shaped leaves that can be distinguished from Ginkgo, Ginkgoites and Baiera by the lack of a petiole. It became extinct about 72.6 million years ago. The family to which this genus belongs has not been conclusively established; an affinity with the Karkeniaceae has been suggested on morphological grounds.

Welwitschia

Welwitschia is a monotypic gymnosperm genus, comprising solely the distinctive Welwitschia mirabilis, endemic to the Namib desert within Namibia and Angola. The plant is commonly known simply as welwitschia in English, but the name tree tumbo is also used. It is called kharos or khurub in Nama, tweeblaarkanniedood in Afrikaans, nyanka in Damara, and onyanga in Herero. Welwitschia is the only living genus of the family Welwitschiaceae and order Welwitschiales, in the division Gnetophyta. Informal sources commonly refer to the plant as a "living fossil".

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