Microsporangia

Microsporangia are sporangia that produce microspores and give rise to male gametes. Microsporangia occur in all plants that have heterosporic life cycles, such as spike mosses. In gymnosperms and angiosperm anthers, the microsporangia produce the microsporocytes, the microspore mother cells, which then produce four microspores through the process of meiosis. In the microsporocyte of Arabidopsis thaliana, meiosis depends on the expression of genes that facilitate DNA repair and homologous recombination.[1] The microspores divide by mitosis to produce pollen grains.

In angiosperms, a very young anther (the part of the stamen that contains the pollen) consists of actively dividing meristematic cells surrounded by a layer of epidermis. It then becomes two-lobed. Each anther lobe develops two pollen sacs. Then, a two-lobed anther develops four pollen sacs that situate at four corners of the anther. Development of pollen sacs begins with the differentiation of archesporial cells in the hypodermal region below epidermis at four corners of the young anther. The archesporial cells divide by periclinal division to give a subepidermal primary parietal layer and a primary sporogenous layer. The cells of the primary parietal layer divide by successive periclinal and anticlinal divisions to form concentric layers of pollen sac wall. The wall layers from periphery to center consist of:

  • A single layer of epidermis between, which becomes stretched and shrivels off at maturity
  • A single layer of endothecium. The cells of endothecium have fibrous thickenings.
  • One to three middle layers. Cells of these layers generally disintegrate in the mature anther
  • A single layer of tapetum. The tapetal cells may be uni-, bi- or multinucleate and possess dense cytoplasm. The cells of the primary sporogenous layer divide further and give rise to diploid sporogenous tissue.

References

  1. ^ Seeliger K, Dukowic-Schulze S, Wurz-Wildersinn R, Pacher M, Puchta H (2012). "BRCA2 is a mediator of RAD51- and DMC1-facilitated homologous recombination in Arabidopsis thaliana". New Phytol. 193 (2): 364–75. doi:10.1111/j.1469-8137.2011.03947.x. PMID 22077663.
Abies balsamea

Abies balsamea or balsam fir is a North American fir, native to most of eastern and central Canada (Newfoundland west to central Alberta) and the northeastern United States (Minnesota east to Maine, and south in the Appalachian Mountains to West Virginia).It is celebrated for its rich green needles, natural conical shape, and needle retention after being cut, and it is notably the most fragrant of all Christmas tree varieties.

Alternation of generations

Alternation of generations (also known as metagenesis) is the type of life cycle that occurs in those plants and algae in the Archaeplastida and the Heterokontophyta that have distinct sexual haploid and asexual diploid stages. In these groups, a multicellular gametophyte, which is haploid with n chromosomes, alternates with a multicellular sporophyte, which is diploid with 2n chromosomes, made up of n pairs. A mature sporophyte produces spores by meiosis, a process which reduces the number of chromosomes to half, from 2n to n.

The haploid spores germinate and grow into a haploid gametophyte. At maturity, the gametophyte produces gametes by mitosis, which does not alter the number of chromosomes. Two gametes (originating from different organisms of the same species or from the same organism) fuse to produce a zygote, which develops into a diploid sporophyte. This cycle, from gametophyte to gametophyte (or equally from sporophyte to sporophyte), is the way in which all land plants and many algae undergo sexual reproduction.

The relationship between the sporophyte and gametophyte varies among different groups of plants. In those algae which have alternation of generations, the sporophyte and gametophyte are separate independent organisms, which may or may not have a similar appearance. In liverworts, mosses and hornworts, the sporophyte is less well developed than the gametophyte and is largely dependent on it. Although moss and hornwort sporophytes can photosynthesise, they require additional photosynthate from the gametophyte to sustain growth and spore development and depend on it for supply of water, mineral nutrients and nitrogen. By contrast, in all modern vascular plants the gametophyte is less well developed than the sporophyte, although their Devonian ancestors had gametophytes and sporophytes of approximately equivalent complexity. In ferns the gametophyte is a small flattened autotrophic prothallus on which the young sporophyte is briefly dependent for its nutrition. In flowering plants, the reduction of the gametophyte is much more extreme; it consists of just a few cells which grow entirely inside the sporophyte.

Animals develop differently. They directly produce haploid gametes. No haploid spores capable of dividing are produced, so they do not have a haploid gametophyte alternating with a diploid sporophyte. (Some insects have a sex-determining system whereby haploid males are produced from unfertilized eggs; however the females are diploid.)

Life cycles of plants and algae with alternating haploid and diploid multicellular stages are referred to as diplohaplontic (the equivalent terms haplodiplontic, diplobiontic or dibiontic are also in use). Life cycles, such as those of animals, in which there is only a diploid multicellular stage are referred to as diplontic. Life cycles in which there is only a haploid multicellular stage are referred to as haplontic.

Amelanchier

Amelanchier ( am-ə-LAN-sheer), also known as shadbush, shadwood or shadblow, serviceberry or sarvisberry, or just sarvis, juneberry, saskatoon, sugarplum or wild-plum, and chuckley pear is a genus of about 20 species of deciduous-leaved shrubs and small trees in the rose family (Rosaceae).

Amelanchier is native to temperate regions of the Northern Hemisphere, growing primarily in early successional habitats. It is most diverse taxonomically in North America, especially in the northeastern United States and adjacent southeastern Canada, and at least one species is native to every U.S. state except Hawaii and to every Canadian province and territory. Two species also occur in Asia, and one in Europe. The taxonomic classification of shadbushes has long perplexed botanists, horticulturalists, and others, as suggested by the range in number of species recognized in the genus, from 6 to 33, in two recent publications. A major source of complexity comes from the occurrence of hybridization, polyploidy, and apomixis (asexual seed production), making species difficult to characterize and identify.The various species of Amelanchier grow to 0.2–20 m tall; some are small trees, some are multistemmed, clump-forming shrubs, and yet others form extensive low shrubby patches (clones). The bark is gray or less often brown, and in tree species smooth or fissuring when older. The leaves are deciduous, cauline, alternate, simple, lanceolate to elliptic to orbiculate, 0.5–10 x 0.5–5.5 cm, thin to coriaceous, with surfaces above glabrous or densely tomentose at flowering, and glabrous or more or less hairy beneath at maturity. The inflorescences are terminal, with 1–20 flowers, erect or drooping, either in clusters of one to four flowers, or in racemes with 4–20 flowers. The flowers have five white (rarely somewhat pink, yellow, or streaked with red), linear to orbiculate petals, 2.6–25 mm long, with the petals in one species (A. nantucketensis) often andropetalous (bearing apical microsporangia adaxially). The flowers appear in early spring, "when the shad run" according to North-American tradition (leading to names such as "shadbush"). The fruit is a berry-like pome, red to purple to nearly black at maturity, 5–15 mm diameter, insipid to delectably sweet, maturing in summer.Amelanchier plants are valued horticulturally, and their fruits are important to wildlife.

Antheridium

An antheridium is a haploid structure or organ producing and containing male gametes (called antherozoids or sperm). The plural form is antheridia, and a structure containing one or more antheridia is called an androecium. "Androecium" is also used as the collective term for the stamens of flowering plants.

Antheridia are present in the gametophyte phase of cryptogams like bryophytes and ferns. Many algae and some fungi, for example ascomycetes and water moulds, also have antheridia during their reproductive stages. In gymnosperms and angiosperms, the male gametophytes have been reduced to pollen grains and in most of these the antheridia have been reduced to a single generative cell within the pollen grain. During pollination, this generative cell divides and gives rise to sperm cells.

The female counterpart to the antheridium in cryptogams is the archegonium, and in flowering plants is the gynoecium.

An antheridium typically consists of sterile cells and spermatogenous tissue. The sterile cells may form a central support structure or surround the spermatogenous tissue as a protective jacket. The spermatogenous cells give rise to spermatids via mitotic cell division. In some bryophytes, the antheridium is borne on an antheridiophore, a stalk-like structure that carries the antheridium at its apex.

Asterotheca

Asterotheca is a genus of seedless, spore-bearing, vascularized ferns dating from the Carboniferous of the Paleozoic to the Triassic of the Mesozoic.

Bryophyte

Bryophytes are an informal group consisting of three divisions of non-vascular land plants (embryophytes): the liverworts, hornworts and mosses. They are characteristically limited in size and prefer moist habitats although they can survive in drier environments. The bryophytes consist of about 20,000 plant species. Bryophytes produce enclosed reproductive structures (gametangia and sporangia), but they do not produce flowers or seeds. They reproduce via spores. Bryophytes are usually considered to be a paraphyletic group and not a monophyletic group, although some studies have produced contrary results. Regardless of their status, the name is convenient and remains in use as an informal collective term. The term "bryophyte" comes from Greek βρύον, bryon "tree-moss, oyster-green" and φυτόν, phyton "plant".

The defining features of bryophytes are:

Their life cycles are dominated by the gametophyte stage

Their sporophytes are unbranched

They do not have a true vascular tissue containing lignin (although some have specialized tissues for the transport of water)

Conifer cone

A cone (in formal botanical usage: strobilus, plural strobili) is an organ on plants in the division Pinophyta (conifers) that contains the reproductive structures. The familiar woody cone is the female cone, which produces seeds. The male cones, which produce pollen, are usually herbaceous and much less conspicuous even at full maturity. The name "cone" derives from the fact that the shape in some species resembles a geometric cone. The individual plates of a cone are known as scales.

The male cone (microstrobilus or pollen cone) is structurally similar across all conifers, differing only in small ways (mostly in scale arrangement) from species to species. Extending out from a central axis are microsporophylls (modified leaves). Under each microsporophyll is one or several microsporangia (pollen sacs).

The female cone (megastrobilus, seed cone, or ovulate cone) contains ovules which, when fertilized by pollen, become seeds. The female cone structure varies more markedly between the different conifer families, and is often crucial for the identification of many species of conifers.

Cycas micronesica

Cycas micronesica is a type of cycad found in the island of Yap in Micronesia, the Marianas islands of Guam and Rota, and The Republic of Palau. It is commonly known as Federico nut or Fadang in Chamorro. The species, previously lumped with Cycas rumphii or Cycas circinalis, was described in 1994 by Ken Hill. Paleoecological studies have determined that C. micronesica has been present on the island of Guam for about 9,000 years. It is linked with the human degenerative disease Lytico-Bodig disease, which is similar to amyotrophic lateral sclerosis (ALS) through a neurotoxin in the seeds, which were a traditional food source on Guam until the 1960s.

International Association for Plant Taxonomy

The International Association for Plant Taxonomy (IAPT) promotes an understanding of plant biodiversity, facilitates international communication of research between botanists, and oversees matters of uniformity and stability in plant names. The IAPT was founded on July 18, 1950 at the Seventh International Botanical Congress in Stockholm, Sweden. Currently, the IAPT headquarters is located in Bratislava, Slovakia. Its current president, since 2017, is Patrick S. Herendeen (Chicago Botanic Garden); vice-president is Gonzalo Nieto Feliner (Real Jardín Botánico, Madrid); and secretary-general is Karol Marhold (Plant Science and Biodiversity Centre, Slovak Academy of Sciences, Bratislava).

Both the taxonomic journal Taxon and the series Regnum Vegetabile are published by the IAPT. The latter series includes the International Code of Nomenclature for algae, fungi, and plants, Index Nominum Genericorum, and Index Herbariorum.

International Code of Nomenclature for Cultivated Plants

The International Code of Nomenclature for Cultivated Plants (ICNCP), also known as the Cultivated Plant Code, is a guide to the rules and regulations for naming cultigens, plants whose origin or selection is primarily due to intentional human activity. Cultigens under the purview of the ICNCP include cultivars, Groups (cultivar groups), and grexes. All organisms traditionally considered to be plants (including algae and fungi) are included. Taxa that receive a name under the ICNCP will also be included within taxa named under the International Code of Nomenclature for algae, fungi, and plants, for example, a cultivar is a member of a species.

Microspore

Microspores are land plant spores that develop into male gametophytes, whereas megaspores develop into female gametophytes. The male gametophyte gives rise to sperm cells, which are used for fertilization of an egg cell to form a zygote. Megaspores are structures that are part of the alternation of generations in many seedless vascular cryptogams, all gymnosperms and all angiosperms. Plants with heterosporous life cycles using microspores and megaspores arose independently in several plant groups during the Devonian period. Microspores are haploid, and are produced from diploid microsporocytes by meiosis.

Raceme

A raceme ( or ) is an unbranched, indeterminate type of inflorescence bearing pedicellate flowers (flowers having short floral stalks called pedicels) along its axis. In botany, an axis means a shoot, in this case one bearing the flowers. In indeterminate inflorescence-like racemes, the oldest flowers are borne towards the base and new flowers are produced as the shoot grows, with no predetermined growth limit. A plant that flowers on a showy raceme may have this reflected in its scientific name, e.g. Cimicifuga racemosa. A compound raceme, also called a panicle, has a branching main axis. Examples of racemes occur on mustard (genus Brassica) and radish (genus Raphanus) plants.

Salvinia

Salvinia, a genus in the family Salviniaceae, is a floating fern named in honor of Anton Maria Salvini, a 17th-century Italian scientist. Watermoss is a common name for Salvinia. The genus was published in 1754 by Jean-François Séguier, in his description of the plants found round Verona, Plantae Veronenses Twelve species are recognized, at least three of which (S. molesta, S. herzogii, and S. minima) are believed to be hybrids, in part because their sporangia are found to be empty.

Salvinia is related to the other water ferns, including the mosquito fern Azolla. Recent sources include both Azolla and Salvinia in Salviniaceae, although each genus was formerly given its own family.

Salvinia, like the other ferns in order Salviniales, are heterosporous, producing spores of differing sizes. However, leaf development in Salvinia is unique. The upper side of the floating leaf, which appears to face the stem axis, is morphologically abaxial.From a human point of view, when their growth is robust the plants pose a particular hindrance on lakes. For example, they choked off much of the water in Lake Bistineau near Doyline in Webster Parish, Louisiana and affected a second Webster Parish site, Caney Lakes Recreation Area.Salvinia cucullata is one of just two fern species for which a reference genome has been published.

Sporangium

A sporangium (pl., sporangia) (modern Latin, from Greek σπόρος (sporos) ‘spore’ + ἀγγεῖον (angeion) ‘vessel’) is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. All plants, fungi, and many other lineages form sporangia at some point in their life cycle. Sporangia can produce spores by mitosis, but in nearly all land plants and many fungi, sporangia are the site of meiosis and produce genetically distinct haploid spores.

Sporocarp (ferns)

A sporocarp is a specialised type of structure found in some ferns whose primary function is the production and release of spores.

Among ferns, sporocarps are found only in the three families of the order Salviniales, a group that is both aquatic and heterosporous. The term actually refers to two very different structures. In the Azollaceae and Salviniaceae, the sporocarp is nothing more than a modified sorus, a single cluster of spore-producing tissues enclosed by a thin sphere of tissue and attached to the leaves.

In the Marsileaceae (water-clover family), however, the sporocarp is a more elaborate structure formed from an entire leaf whose development and form is greatly modified. These are hairy, short-stalked, bean-shaped structures (usually 3 to 8 mm in diameter) with a hardened outer covering. This outer covering is tough and resistant to drying out, allowing the spores inside to survive unfavorable conditions such as winter frost or summer desiccation. Despite this toughness, the sporocarps will open readily in water if conditions are favorable, and specimens have been successfully germinated after being stored for more than forty years. Each growing season, only one sporocarp develops per node along the rhizome near the base of the other leaf-stalks.

The sporocarps are functionally and developmentally modified leaves, although they have much shorter stalks than the vegetative leaves. Inside the sporocarp, the modified leaflets bear several sori, each of which consists of several sporangia covered by a thin hood of tissue (the indusium). Each sorus includes a mix of two types of sporangium, each type producing only one of two kinds of spores. Toward the center of each sorus and developing first are the megasporangia, each of which will produce a single large female megaspore. Surrounding them at the edge of the sorus and developing later are the microsporangia, each of which will produce many small male microspores.

Sporophyll

A sporophyll is a leaf that bears sporangia. Both microphylls and megaphylls can be sporophylls. In heterosporous plants, sporophylls (whether they are microphylls or megaphylls) bear either megasporangia and thus are called megasporophylls, or microsporangia and are called microsporophylls. The overlap of the prefixes and roots makes these terms a particularly confusing subset of botanical nomenclature.

Sporophylls vary greatly in appearance and structure, and may or may not look similar to sterile leaves. Plants that produce sporophylls include:

Alaria esculenta a brown alga shows sporophylls attached near the base of the alga.Lycophytes, where sporophylls may be aggregated into strobili (Selaginella and some Lycopodium and related genera) or distributed singly among sterile leaves (Huperzia). Sporangia are borne in the axil or on the adaxial surface of the sporophyll. In heterosporous members, megasporophylls and microsporophylls may be intermixed or separated in a variety of patterns.

Ferns, which may produce sporophylls that are similar to sterile fronds or that appear very different from sterile fronds. These may be non-photosynthetic and lack typical pinnae (e.g. Onoclea)

Cycads produce strobili, both pollen-producing and seed-producing, that are composed of sporophylls.

Ginkgo produces microsporophylls aggregated into a pollen strobilus. Ovules are not born on sporophylls.

Conifers, like Ginkgo and cycads, produce microsporophylls, aggregated into pollen strobili. However, unlike these other groups, ovules are produced on cone scales, which are modified shoots rather than sporophylls.

Some plants do not produce sporophylls. Sporangia are produced directly on stems. Psilotum has been interpreted as producing sporangia (fused in a synangium) on the terminus of a stem. Equisetum always produce strobili, but the structures bearing sporangia (sporangiophores) have been interpreted as modified stems. The sporangia, despite being recurved are interpreted as terminal.

Gnetophytes produce both compound pollen and seed strobili.

Stamen

The stamen (plural stamina or stamens) is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium.

Strobilus

A strobilus (plural: strobili) is a structure present on many land plant species consisting of sporangia-bearing structures densely aggregated along a stem. Strobili are often called cones, but many botanists restrict the use of the term cone to the woody seed strobili of conifers. Strobili are characterized by a central axis (anatomically a stem) surrounded by spirally arranged or decussate structures that may be modified leaves or modified stems.

Leaves that bear sporangia are called sporophylls, while sporangia-bearing stems are called sporangiophores.

Theca

A theca (plural thecae) refers to a sheath or a covering.

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