Gymnosperm

'' cone Over 1,000 living species of gymnosperm exist. It was previously widely accepted that the gymnosperms originated in the Late Carboniferous period, replacing the lycopsid rainforests of the tropical region, but more recent phylogenetic evidence indicates that they diverged from the ancestors of angiosperms during the Early Carboniferous. The radiation of gymnosperms during the late Carboniferous appears to have resulted from a whole genome duplication event around . Early characteristics of seed plants are 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 proboscides 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. Some mid-Mesozoic gymnosperms were pollinated by kalligrammatid lacewings. All gymnosperms are perennial woody plants. 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 gymnosperms and compared to angiosperms they occupy fewer ecological niches, but the gymnosperms include parasites (Parasitaxus), epiphytes (Zamia pseudoparasitica) and rheophytes (Retrophyllum minus). 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). Most conifers are evergreens. Conifers produce their seeds inside a protective cone called a strobilus. Most species are monoecious, with male and female cones on the same tree. All conifers are wind-pollinated. Cycads, small palm-like trees, ==Classification==

{{cladogram|title=Phylogeny of Gymnosperms| {{clade|style=font-size:90%;line-height:80%;width:400px |1= |2={{Clade |label1x=Pinidae |1={{Clade |1= |label2= |2={{Clade |label1=Araucariales |1={{Clade |label1=Araucariaceae |1= |label2=Podocarpaceae |2={{Clade |1={"Phyllocladoideae"} |2={"Podocarpoideae"} }} }} |label2=Cupressales |2={{Clade |1= |2={{Clade |label1=Taxaceae |1= |label2=Cupressaceae |2={{Clade |1= |2={{Clade |1= |2={{Clade |1= |2={{Clade |1= |2={{Clade |1= |2={{Clade |1={"Actinostroboideae"} |2={"Cupressoideae"} }} }} }} }} }} }} }} }} }} }} }} }} |1=Halocarpus |2= }} }} |1=Saxegothaea |2= }} }} |1=Papuacedrus |2= }} }} |1= |2= }} }} }} }} A formal classification of the living gymnosperms is the "Acrogymnospermae", which form a monophyletic group within the spermatophytes. 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). 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. Subclass Cycadidae • Order Cycadales • Family Cycadaceae: Cycas • Family Zamiaceae: Dioon, Bowenia, Macrozamia, Lepidozamia, Encephalartos, Stangeria, Ceratozamia, Microcycas, Zamia Subclass Ginkgoidae • Order Ginkgoales • Family Ginkgoaceae: Ginkgo Subclass Gnetidae • Order Welwitschiales • Family Welwitschiaceae: Welwitschia • Order Gnetales • Family Gnetaceae: Gnetum • Order Ephedrales • Family Ephedraceae: Ephedra 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 Extinct groupings • Order Cordaitales • Order Calamopityales • Order Callistophytales • Order Caytoniales • Order Gigantopteridales • Order Glossopteridales • Order Lyginopteridales • Order Medullosales • Order Peltaspermales • Order Corystospermales (also known as Umkomasiales) • Order Czekanowskiales • Order Bennettitales (cycadeoids) • Order Erdtmanithecales • Order Pentoxylales • Order Petriellales ==Life cycle==

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. Like all seed plants, they are heterosporous, having two spore types, microspores (male) produced in microsporangium and megaspores (female) produced in megasporangium that are typically present in pollen cones or ovulate cones respectively. The microsporangium is carried by microsporophyll (modified leaf) and seeds are carried by ovuliferous scales in the male and female cones respectively. The exception is the females in the cycad genus Cycas, which form a loose structure called megasporophylls instead of cones. As with all heterosporous plants, the gametophytes 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 gametes. 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. Gymnosperms ordinarily reproduce by sexual reproduction, and only rarely express parthenogenesis. Sexual reproduction in gymnosperms appears to be required for maintaining long-term genomic integrity. ==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 perfumes. == References ==