The Embryophyta, or land plants, are the most familiar group of green plants that form vegetation on earth. Embryophyta is a clade within the Phragmoplastophyta, a larger clade that also includes several green algae groups (including the Charophyceae and Coleochaetales), and within this large clade the embryophytes are sister to the Zygnematophyceae/Mesotaeniaceae and consist of the bryophytes plus the polysporangiophytes. Living embryophytes therefore include hornworts, liverworts, mosses, ferns, lycophytes, gymnosperms and flowering plants. The Embryophyta are informally called land plants because they live primarily in terrestrial habitats, while the related green algae are primarily aquatic. Embryophytes are complex multicellular eukaryotes with specialized reproductive organs. The name derives from their innovative characteristic of nurturing the young embryo sporophyte during the early stages of its multicellular development within the tissues of the parent gametophyte. With very few exceptions, embryophytes obtain their energy by photosynthesis, that is by using the energy of sunlight to synthesize their food from carbon dioxide and water.
The evolutionary origins of the embryophytes are discussed further below, but they are believed to have evolved from within a group of complex green algae during the Paleozoic era (which started around ) probably from terrestrial unicellular charophytes, similar to extant Klebsormidiophyceae. Embryophytes are primarily adapted for life on land, although some are secondarily aquatic. Accordingly, they are often called land plants or terrestrial plants.
On a microscopic level, the cells of embryophytes are broadly similar to those of green algae, but differ in that in cell division the daughter nuclei are separated by a phragmoplast. They are eukaryotic, with a cell wall composed of cellulose and plastids surrounded by two membranes. The latter include chloroplasts, which conduct photosynthesis and store food in the form of starch, and are characteristically pigmented with chlorophylls a and b, generally giving them a bright green color. Embryophyte cells also generally have an enlarged central vacuole enclosed by a vacuolar membrane or tonoplast, which maintains cell turgor and keeps the plant rigid.
In common with all groups of multicellular algae they have a life cycle which involves 'alternation of generations'. A multicellular generation with a single set of chromosomes – the haploid gametophyte – produces sperm and eggs which fuse and grow into a multicellular generation with twice the number of chromosomes – the diploid sporophyte. The mature sporophyte produces haploid spores which grow into a gametophyte, thus completing the cycle. Embryophytes have two features related to their reproductive cycles which distinguish them from all other plant lineages. Firstly, their gametophytes produce sperm and eggs in multicellular structures (called 'antheridia' and 'archegonia'), and fertilization of the ovum takes place within the archegonium rather than in the external environment. Secondly, and most importantly, the initial stage of development of the fertilized egg (the zygote) into a diploid multicellular sporophyte, take place within the archegonium where it is both protected and provided with nutrition. This second feature is the origin of the term 'embryophyte' – the fertilized egg develops into a protected embryo, rather than dispersing as a single cell. In the bryophytes the sporophyte remains dependent on the gametophyte, while in all other embryophytes the sporophyte generation is dominant and capable of independent existence.
Embryophytes also differ from algae by having metamers. Metamers are repeated units of development, in which each unit derives from a single cell, but the resulting product tissue or part is largely the same for each cell. The whole organism is thus constructed from similar, repeating parts or metamers. Accordingly, these plants are sometimes termed 'metaphytes' and classified as the group Metaphyta (but Haeckel's definition of Metaphyta places some algae in this group). In all land plants a disc-like structure called a phragmoplast forms where the cell will divide, a trait only found in the land plants in the streptophyte lineage, some species within their relatives Coleochaetales, Charales and Zygnematales, as well as within subaerial species of the algae order Trentepohliales, and appears to be essential in the adaptation towards a terrestrial life style.
All green algae and land plants are now known to form a single evolutionary lineage or clade, one name for which is Viridiplantae (i.e. 'green plants'). According to several molecular clock estimates the Viridiplantae split to into two clades: chlorophytes and streptophytes. The chlorophytes are considerably more diverse (with around 700 genera) and were originally marine, although some groups have since spread into fresh water. The streptophyte algae (i.e. the streptophyte clade minus the land plants) are less diverse (with around 122 genera) and adapted to fresh water very early in their evolutionary history. They have not spread into marine environments (only a few stoneworts, which belong to this group, tolerate brackish water). Some time during the Ordovician period (which started around ) one or more streptophytes invaded the land and began the evolution of the embryophyte land plants. Present day embryophytes form a monophyletic group called the hemitracheophytes.
Becker and Marin speculate that land plants evolved from streptophytes rather than any other group of algae because streptophytes were adapted to living in fresh water. This prepared them to tolerate a range of environmental conditions found on land. Fresh water living made them tolerant of exposure to rain; living in shallow pools required tolerance to temperature variation, high levels of ultra-violet light and seasonal dehydration.
Relationships between the groups making up Viridiplantae are still being elucidated. Views have changed considerably since 2000 and classifications have not yet caught up. However, the division between chlorophytes and streptophytes and the evolution of embryophytes from within the latter group, as shown in the cladogram below, are well established. Three approaches to classification are shown. Older classifications, as on the left, treated all green algae as a single division of the plant kingdom under the name Chlorophyta. Land plants were then placed in separate divisions. All the streptophyte algae can be grouped into one paraphyletic taxon, as in the middle, allowing the embryophytes to form a taxon at the same level. Alternatively, the embryophytes can be sunk into a monophyletic taxon comprising all the streptophytes, as shown below. A variety of names have been used for the different groups which result from these approaches; those used below are only one of a number of possibilities. The higher-level classification of the Viridiplantae varies considerably, resulting in widely different ranks being assigned to the embryophytes, from kingdom to class.
The precise relationships within the streptophytes are less clear as of March 2012. The stoneworts (Charales) have traditionally been identified as closest to the embryophytes, but recent work suggests that either the Zygnematales or a clade consisting of the Zygnematales and the Coleochaetales may be the sister group to the land plants. That the Zygnematales (or Zygnematophyceae) are the closest algal relatives to land plants was underpinned by an exhaustive phylogenetic analysis (phylogenomics) performed in 2014, which is supported by both plastid genome phylogenies as well as plastid gene content and properties.
The preponderance of molecular evidence as of 2006 suggested that the groups making up the embryophytes are related as shown in the cladogram below (based on Qiu et al. 2006 with additional names from Crane et al. 2004).
Studies based on morphology rather than on genes and proteins have regularly reached different conclusions; for example that neither the monilophytes (ferns and horsetails) nor the gymnosperms are a natural or monophyletic group.
There is considerable variation in how these relationships are converted into a formal classification. Consider the angiosperms or flowering plants. Many botanists, following Lindley in 1830, have treated the angiosperms as a division. Palaeobotanists have usually followed Banks in treating the tracheophytes or vascular plants as a division, so that the angiosperms become a class or even a subclass. Two very different systems are shown below. The classification on the left is a traditional one, in which ten living groups are treated as separate divisions; the classification on the right (based on Kenrick and Crane's 1997 treatment) sharply reduces the rank of groups such as the flowering plants. (More complex classifications are needed if extinct plants are included.)
|Ferns and horsetails||Pteridophyta||Moniliformopses|
An updated phylogeny of Embryophyta based on the work by Novíkov & Barabaš-Krasni 2015 with plant taxon authors from Anderson, Anderson & Cleal 2007 and some clade names from Pelletier 2012 and others. Puttick et al./Nishiyama et al are used for the basal clades.
Bryophytes consist of all non-vascular land plants (embryophytes without vascular tissue). All are relatively small and are usually confined to environments that are humid or at least seasonally moist. They are limited by their reliance on water needed to disperse their gametes, although only a few bryophytes are truly aquatic. Most species are tropical, but there are many arctic species as well. They may locally dominate the ground cover in tundra and Arctic–alpine habitats or the epiphyte flora in rain forest habitats.
The three living divisions are the mosses (Bryophyta), hornworts (Anthocerotophyta), and liverworts (Marchantiophyta). Originally, these three groups were included together as classes within the single division Bryophyta. However, they are now usually placed separately into three divisions since the bryophytes as a whole are thought to be a paraphyletic (artificial) group instead of a single lineage. The three bryophyte groups form an evolutionary grade of those land plants that are not vascular. Some closely related green algae are also non-vascular, but are not considered "land plants".
Regardless of their evolutionary origins, the bryophytes are usually studied together because of their many biological similarities as non-vascular land plants. All three bryophyte groups share a haploid-dominant (gametophyte) life cycle and unbranched sporophytes (the plant's diploid structure). These are traits that appear to be plesiotypic within the land plants, and thus were common to all early diverging lineages of plants on the land. The fact that the bryophytes have a life cycle in common may thus be an artefact of being the oldest extant lineages of land plant, and not the result of close shared ancestry. (See the phylogeny above.)
The bryophyte life-cycle is strongly dominated by the haploid gametophyte generation. The sporophyte remains small and dependent on the parent gametophyte for its entire brief life. All other living groups of land plants have a life cycle dominated by the diploid sporophyte generation. It is in the diploid sporophyte that vascular tissue develops. Although some mosses have quite complex water-conducting vessels, bryophytes lack true vascular tissue.
Like the vascular plants, bryophytes do have differentiated stems, and although these are most often no more than a few centimeters tall, they do provide mechanical support. Most bryophytes also have leaves, although these typically are one cell thick and lack veins. Unlike the vascular plants, bryophytes lack true roots or any deep anchoring structures. Some species do grow a filamentous network of horizontal stems, but these have a primary function of mechanical attachment rather than extraction of soil nutrients (Palaeos 2008).
During the Silurian and Devonian periods (around ), plants evolved which possessed true vascular tissue, including cells with walls strengthened by lignin (tracheids). Some extinct early plants appear to be between the grade of organization of bryophytes and that of true vascular plants (eutracheophytes). Genera such as Horneophyton have water-conducting tissue more like that of mosses, but a different life-cycle in which the sporophyte is more developed than the gametophyte. Genera such as Rhynia have a similar life-cycle but have simple tracheids and so are a kind of vascular plant. It was assumed that the gametophyte dominant phase seen in bryophytes used to be the ancestral condition in terrestrial plants, and that the sporophyte dominant stage in vascular plants was a derived trait. But research point out the possibility that both the gametophyte and sporophyte stage were equally independent from each other, and that the mosses and vascular plants in that case are both derived, and has evolved in the opposite direction from the other.
During the Devonian period, vascular plants diversified and spread to many different land environments. In addition to vascular tissues which transport water throughout the body, tracheophytes have an outer layer or cuticle that resists drying out. The sporophyte is the dominant generation, and in modern species develops leaves, stems and roots, while the gametophyte remains very small.
All the vascular plants which disperse through spores were once thought to be related (and were often grouped as 'ferns and allies'). However, recent research suggests that leaves evolved quite separately in two different lineages. The lycophytes or lycopodiophytes – modern clubmosses, spikemosses and quillworts – make up less than 1% of living vascular plants. They have small leaves, often called 'microphylls' or 'lycophylls', which are borne all along the stems in the clubmosses and spikemosses, and which effectively grow from the base, via an intercalary meristem. It is believed that microphylls evolved from outgrowths on stems, such as spines, which later acquired veins (vascular traces).
Although the living lycophytes are all relatively small and inconspicuous plants, more common in the moist tropics than in temperate regions, during the Carboniferous period tree-like lycophytes (such as Lepidodendron) formed huge forests that dominated the landscape.
The euphyllophytes, making up more than 99% of living vascular plant species, have large 'true' leaves (megaphylls), which effectively grow from the sides or the apex, via marginal or apical meristems. One theory is that megaphylls developed from three-dimensional branching systems by first 'planation' – flattening to produce a two dimensional branched structure – and then 'webbing' – tissue growing out between the flattened branches. Others have questioned whether megaphylls developed in the same way in different groups.
Euphyllophytes are divided into two lineages: the ferns and horsetails (monilophytes) and the seed plants (spermatophytes). Like all the preceding groups, the monilophytes continue to use spores as their main method of dispersal. Traditionally, whisk ferns and horsetails were treated as distinct from 'true' ferns. Recent research suggests that they all belong together, although there are differences of opinion on the exact classification to be used. Living whisk ferns and horsetails do not have the large leaves (megaphylls) which would be expected of euphyllophytes. However, this has probably resulted from reduction, as evidenced by early fossil horsetails, in which the leaves are broad with branching veins.
Seed plants, which first appeared in the fossil record towards the end of the Paleozoic era, reproduce using desiccation-resistant capsules called seeds. Starting from a plant which disperses by spores, highly complex changes are needed to produce seeds. The sporophyte has two kinds of spore-forming organs (sporangia). One kind, the megasporangium, produces only a single large spore (a megaspore). This sporangium is surrounded by one or more sheathing layers (integuments) which form the seed coat. Within the seed coat, the megaspore develops into a tiny gametophyte, which in turn produces one or more egg cells. Before fertilization, the sporangium and its contents plus its coat is called an 'ovule'; after fertilization a 'seed'. In parallel to these developments, the other kind of sporangium, the microsporangium, produces microspores. A tiny gametophyte develops inside the wall of a microspore, producing a pollen grain. Pollen grains can be physically transferred between plants by the wind or animals, most commonly insects. Pollen grains can also transfer to an ovule of the same plant, either with the same flower or between two flowers of the same plant (self-fertilization). When a pollen grain reaches an ovule, it enters via a microscopic gap in the coat (the micropyle). The tiny gametophyte inside the pollen grain then produces sperm cells which move to the egg cell and fertilize it. Seed plants include two groups with living members, the gymnosperms and the angiosperms or flowering plants. In gymnosperms, the ovules or seeds are not further enclosed. In angiosperms, they are enclosed in ovaries. A split ovary with a visible seed can be seen in the adjacent image. Angiosperms typically also have other, secondary structures, such as petals, which together form a flower.
Extant seed plants are divided into five groups:
Blackberry Hill is a series of quarries and outcrops in Central Wisconsin that is notable for its large concentration of trace fossils in Cambrian rocks. One quarry in particular, located in Marathon County, also has the distinction of preserving some of the first land animals. The site is a prolific Cambrian Konservat-Lagerstätte. It includes three-dimensional casts of soft bodied and lightly scleritized invertebrates and a variety of exceptionally preserved types of trace fossils.Botany
Botany, also called plant science(s), plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the Ancient Greek word βοτάνη (botanē) meaning "pasture", "grass", or "fodder"; βοτάνη is in turn derived from βόσκειν (boskein), "to feed" or "to graze". Traditionally, botany has also included the study of fungi and algae by mycologists and phycologists respectively, with the study of these three groups of organisms remaining within the sphere of interest of the International Botanical Congress. Nowadays, botanists (in the strict sense) study approximately 410,000 species of land plants of which some 391,000 species are vascular plants (including approximately 369,000 species of flowering plants), and approximately 20,000 are bryophytes.Botany originated in prehistory as herbalism with the efforts of early humans to identify – and later cultivate – edible, medicinal and poisonous plants, making it one of the oldest branches of science. Medieval physic gardens, often attached to monasteries, contained plants of medical importance. They were forerunners of the first botanical gardens attached to universities, founded from the 1540s onwards. One of the earliest was the Padua botanical garden. These gardens facilitated the academic study of plants. Efforts to catalogue and describe their collections were the beginnings of plant taxonomy, and led in 1753 to the binomial system of Carl Linnaeus that remains in use to this day.
In the 19th and 20th centuries, new techniques were developed for the study of plants, including methods of optical microscopy and live cell imaging, electron microscopy, analysis of chromosome number, plant chemistry and the structure and function of enzymes and other proteins. In the last two decades of the 20th century, botanists exploited the techniques of molecular genetic analysis, including genomics and proteomics and DNA sequences to classify plants more accurately.
Modern botany is a broad, multidisciplinary subject with inputs from most other areas of science and technology. Research topics include the study of plant structure, growth and differentiation, reproduction, biochemistry and primary metabolism, chemical products, development, diseases, evolutionary relationships, systematics, and plant taxonomy. Dominant themes in 21st century plant science are molecular genetics and epigenetics, which are the mechanisms and control of gene expression during differentiation of plant cells and tissues. Botanical research has diverse applications in providing staple foods, materials such as timber, oil, rubber, fibre and drugs, in modern horticulture, agriculture and forestry, plant propagation, breeding and genetic modification, in the synthesis of chemicals and raw materials for construction and energy production, in environmental management, and the maintenance of biodiversity.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)Cambrian
The Cambrian Period ( or ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 55.6 million years from the end of the preceding Ediacaran Period 541 million years ago (mya) to the beginning of the Ordovician Period 485.4 mya. Its subdivisions, and its base, are somewhat in flux. The period was established (as “Cambrian series”) by Adam Sedgwick, who named it after Cambria, the Latin name of Wales, where Britain's Cambrian rocks are best exposed. The Cambrian is unique in its unusually high proportion of lagerstätte sedimentary deposits, sites of exceptional preservation where "soft" parts of organisms are preserved as well as their more resistant shells. As a result, our understanding of the Cambrian biology surpasses that of some later periods.The Cambrian marked a profound change in life on Earth; prior to the Cambrian, the majority of living organisms on the whole were small, unicellular and simple; the Precambrian Charnia being exceptional. Complex, multicellular organisms gradually became more common in the millions of years immediately preceding the Cambrian, but it was not until this period that mineralized—hence readily fossilized—organisms became common. The rapid diversification of life forms in the Cambrian, known as the Cambrian explosion, produced the first representatives of all modern animal phyla. Phylogenetic analysis has supported the view that during the Cambrian radiation, metazoa (animals) evolved monophyletically from a single common ancestor: flagellated colonial protists similar to modern choanoflagellates.
Although diverse life forms prospered in the oceans, the land is thought to have been comparatively barren—with nothing more complex than a microbial soil crust and a few molluscs that emerged to browse on the microbial biofilm. Most of the continents were probably dry and rocky due to a lack of vegetation. Shallow seas flanked the margins of several continents created during the breakup of the supercontinent Pannotia. The seas were relatively warm, and polar ice was absent for much of the period.Chlorophyta
Chlorophyta or Prasinophyta is a taxon of green algae informally called chlorophytes. The name is used in two very different senses, so care is needed to determine the use by a particular author. In older classification systems, it refers to a highly paraphyletic group of all the green algae within the green plants (Viridiplantae) and thus includes about 7,000 species of mostly aquatic photosynthetic eukaryotic organisms. In newer classifications, it refers to the sister of the streptophytes/charophytes. The clade Streptophyta consists of the Charophyta in which the Embryophyta emerged. In this sense the Chlorophyta includes only about 4,300 species. About 90% of all known species live in freshwater.
Like the land plants (bryophytes and tracheophytes), green algae contain chlorophyll a and chlorophyll b and store food as starch in their plastids.
With the exception of Palmophyllophyceae, Trebouxiophyceae, Ulvophyceae and Chlorophyceae, which show various degrees of multicellularity, all the Chlorophyta lineages are unicellular. Some members of the group form symbiotic relationships with protozoa, sponges, and cnidarians. Others form symbiotic relationships with fungi to form lichens, but the majority of species are free-living. Some conduct sexual reproduction, which is oogamous or isogamous. All members of the clade have motile flagellated swimming cells. While most species live in freshwater habitats and a large number in marine habitats, other species are adapted to a wide range of land environments. For example, Chlamydomonas nivalis, which causes Watermelon snow, lives on summer alpine snowfields. Others, such as Trentepohlia species, live attached to rocks or woody parts of trees. Monostroma kuroshiense, an edible green alga cultivated worldwide and most expensive among green algae, belongs to this group.Evolutionary history of plants
The evolution of plants has resulted in a wide range of complexity, from the earliest algal mats, through multicellular marine and freshwater green algae, terrestrial bryophytes, lycopods and ferns, to the complex gymnosperms and angiosperms of today. While many of the earliest groups continue to thrive, as exemplified by red and green algae in marine environments, more recently derived groups have displaced previously ecologically dominant ones, e.g. the ascendance of flowering plants over gymnosperms in terrestrial environments.There is evidence that cyanobacteria and multicellular photosynthetic eukaryotes lived in freshwater communities on land as early as 1 billion years ago, and that communities of complex, multicellular photosynthesizing organisms existed on land in the late Precambrian, around 850 million years ago.Evidence of the emergence of embryophyte land plants first occurs in the mid-Ordovician (~470 million years ago), and by the middle of the Devonian (~390 million years ago), many of the features recognised in land plants today were present, including roots and leaves. By Late Devonian (~370 million years ago) some free-sporing plants such as Archaeopteris had secondary vascular tissue that produced wood and had formed forests of tall trees. Also by late Devonian, Elkinsia, an early seed fern, had evolved seeds.
Evolutionary innovation continued throughout the rest of the Phanerozoic eon and still continues today. Most plant groups were relatively unscathed by the Permo-Triassic extinction event, although the structures of communities changed. This may have set the scene for the appearance of the flowering plants in the Triassic (~200 million years ago), and their later diversification in the Cretaceous and Paleogene. The latest major group of plants to evolve were the grasses, which became important in the mid-Paleogene, from around 40 million years ago. The grasses, as well as many other groups, evolved new mechanisms of metabolism to survive the low CO2 and warm, dry conditions of the tropics over the last 10 million years.Green algae
The green algae (singular: green alga) are a large, informal grouping of algae consisting of the Chlorophyta and Charophyta/Streptophyta, which are now placed in separate divisions, as well as the potentially more basal Mesostigmatophyceae, Chlorokybophyceae and Spirotaenia.The land plants, or embryophytes, are thought to have emerged from the charophytes. Therefore, cladistically, embryophytes belong to green algae as well. However, because the embryophytes are traditionally classified as neither algae nor green algae, green algae are a paraphyletic group. Since the realization that the embryophytes emerged from within the green algae, some authors are starting to include them. The clade that includes both green algae and embryophytes is monophyletic and is referred to as the clade Viridiplantae and as the kingdom Plantae. The green algae include unicellular and colonial flagellates, most with two flagella per cell, as well as various colonial, coccoid and filamentous forms, and macroscopic, multicellular seaweeds. There are about 8,000 species of green algae. Many species live most of their lives as single cells, while other species form coenobia (colonies), long filaments, or highly differentiated macroscopic seaweeds.
A few other organisms rely on green algae to conduct photosynthesis for them. The chloroplasts in euglenids and chlorarachniophytes were acquired from ingested green algae, and in the latter retain a nucleomorph (vestigial nucleus). Green algae are also found symbiotically in the ciliate Paramecium, and in Hydra viridissima and in flatworms. Some species of green algae, particularly of genera Trebouxia of the class Trebouxiophyceae and Trentepohlia (class Ulvophyceae), can be found in symbiotic associations with fungi to form lichens. In general the fungal species that partner in lichens cannot live on their own, while the algal species is often found living in nature without the fungus. Trentepohlia is a filamentous green alga that can live independently on humid soil, rocks or tree bark or form the photosymbiont in lichens of the family Graphidaceae. Also the macroalga Prasiola calophylla (Trebouxiophyceae) is terrestrial, and
Prasiola crispa, which live in the supralittoral zone, is terrestrial and can in the Antarctic form large carpets on humid soil, especially near bird colonies.Hollandophyton
Hollandophyton is a genus of extinct plants known from fossils found in Shropshire, England, in rocks of upper Silurian age (Přídolí, around 430 to 420 million years ago). The specimens are fragmentary, consisting of leafless stems (axes) which branched dichotomously and bore kidney-shaped spore-forming organs or sporangia, apparently at their tips. The internal structure of the stems is unknown.Hornwort
Hornworts are a group of non-vascular plants constituting the division Anthocerotophyta. The common name refers to the elongated horn-like structure, which is the sporophyte. As in mosses and liverworts, the flattened, green plant body of a hornwort is the gametophyte plant.
Hornworts may be found worldwide, though they tend to grow only in places that are damp or humid. Some species grow in large numbers as tiny weeds in the soil of gardens and cultivated fields. Large tropical and sub-tropical species of Dendroceros may be found growing on the bark of trees.
The total number of species is still uncertain. While there are more than 300 published species names, the actual number could be as low as 100-150 species.List of biodiversity databases
This is a list of biodiversity databases. Biodiversity databases store taxonomic information alone or more commonly also other information like distribution (spatial) data and ecological data, which provide information on the biodiversity of a particular area or group of living organisms. They may store specimen-level information, species-level information, information on nomenclature, or any combination of the above. Most are available online.
Specimen-focused databases contain data about individual specimens, as represented by vouchered museum specimens, collections of specimen photographs, data on field-based specimen observations and morphological or genetic data. Species-focused databases contain information summarised at the species-level. Some species-focused databases attempt to compile comprehensive data about particular species (FishBase), while others focus on particular species attributes, such as checklists of species in a given area (FEOW) or the conservation status of species (CITES or IUCN Red List). Nomenclators act as summaries of taxonomic revisions and set a key between specimen-focused and species-focused databases. They do this because taxonomic revisions use specimen data to determine species limits.Marchantiophyta
The Marchantiophyta (listen) are a division of non-vascular land plants commonly referred to as hepatics or liverworts. Like mosses and hornworts, they have a gametophyte-dominant life cycle, in which cells of the plant carry only a single set of genetic information.
It is estimated that there are about 9000 species of liverworts. Some of the more familiar species grow as a flattened leafless thallus, but most species are leafy with a form very much like a flattened moss. Leafy species can be distinguished from the apparently similar mosses on the basis of a number of features, including their single-celled rhizoids. Leafy liverworts also differ from most (but not all) mosses in that their leaves never have a costa (present in many mosses) and may bear marginal cilia (very rare in mosses). Other differences are not universal for all mosses and liverworts, but the occurrence of leaves arranged in three ranks, the presence of deep lobes or segmented leaves, or a lack of clearly differentiated stem and leaves all point to the plant being a liverwort.
Liverworts are typically small, usually from 2–20 mm wide with individual plants less than 10 cm long, and are therefore often overlooked. However, certain species may cover large patches of ground, rocks, trees or any other reasonably firm substrate on which they occur. They are distributed globally in almost every available habitat, most often in humid locations although there are desert and Arctic species as well. Some species can be a nuisance in shady greenhouses or a weed in gardens.Michael Melkonian
Michael Melkonian (born 1948 in Hamburg) is a German botanist and professor of botany at the University of Cologne.Microorganism
A microorganism, or microbe, is a microscopic organism, which may exist in its single-celled form or in a colony of cells.
The possible existence of unseen microbial life was suspected from ancient times, such as in Jain scriptures from 6th century BC India and the 1st century BC book On Agriculture by Marcus Terentius Varro. Microbiology, the scientific study of microorganisms, began with their observation under the microscope in the 1670s by Antonie van Leeuwenhoek. In the 1850s, Louis Pasteur found that microorganisms caused food spoilage, debunking the theory of spontaneous generation. In the 1880s, Robert Koch discovered that microorganisms caused the diseases tuberculosis, cholera and anthrax.
Microorganisms include all unicellular organisms and so are extremely diverse. Of the three domains of life identified by Carl Woese, all of the Archaea and Bacteria are microorganisms. These were previously grouped together in the two domain system as Prokaryotes, the other being the eukaryotes. The third domain Eukaryota includes all multicellular organisms and many unicellular protists and protozoans. Some protists are related to animals and some to green plants. Many of the multicellular organisms are microscopic, namely micro-animals, some fungi and some algae, but these are not discussed here.
They live in almost every habitat from the poles to the equator, deserts, geysers, rocks and the deep sea. Some are adapted to extremes such as very hot or very cold conditions, others to high pressure and a few such as Deinococcus radiodurans to high radiation environments. Microorganisms also make up the microbiota found in and on all multicellular organisms. A December 2017 report stated that 3.45-billion-year-old Australian rocks once contained microorganisms, the earliest direct evidence of life on Earth.Microbes are important in human culture and health in many ways, serving to ferment foods, treat sewage, produce fuel, enzymes and other bioactive compounds. They are essential tools in biology as model organisms and have been put to use in biological warfare and bioterrorism. They are a vital component of fertile soils. In the human body microorganisms make up the human microbiota including the essential gut flora. They are the pathogens responsible for many infectious diseases and as such are the target of hygiene measures.Moss
Mosses are small flowerless plants that typically form dense green clumps or mats, often in damp or shady locations. The individual plants are usually composed of simple leaves that are generally only one cell thick, attached to a stem that may be branched or unbranched and has only a limited role in conducting water and nutrients. Although some species have conducting tissues, these are generally poorly developed and structurally different from similar tissue found in vascular plants. Mosses do not have seeds and after fertilisation develop sporophytes with unbranched stalks topped with single capsules containing spores. They are typically 0.2–10 cm (0.1–3.9 in) tall, though some species are much larger. Dawsonia, the tallest moss in the world, can grow to 50 cm (20 in) in height.
Mosses are commonly confused with lichens, hornworts, and liverworts. Lichens may superficially look like mosses, and sometimes have common names that include the word "moss" (e.g., "reindeer moss" or "Iceland moss"), but they are not related to mosses. Mosses used to be grouped together with the hornworts and liverworts as "non-vascular" plants in the former division "bryophytes", all of them having the haploid gametophyte generation as the dominant phase of the life cycle. This contrasts with the pattern in all vascular plants (seed plants and pteridophytes), where the diploid sporophyte generation is dominant.
Mosses are now classified on their own as the division Bryophyta. There are approximately 12,000 species.The main commercial significance of mosses is as the main constituent of peat (mostly the genus Sphagnum), although they are also used for decorative purposes, such as in gardens and in the florist trade. Traditional uses of mosses included as insulation and for the ability to absorb liquids up to 20 times their weight.Pteridophyte
A pteridophyte is a vascular plant (with xylem and phloem) that reproduces using spores. Because pteridophytes produce neither flowers nor seeds, they are also referred to as "cryptogams", meaning that their means of reproduction is hidden. The pteridophytes include the ferns, horsetails, and the lycophytes (clubmosses, spikemosses, and quillworts). These are not a monophyletic group because ferns and horsetails are more closely related to seed plants than to the lycophytes. Therefore, "Pteridophyta" is no longer a widely accepted taxon, although the term pteridophyte remains in common parlance, as do pteridology and pteridologist as a science and its practitioner, to indicate lycophytes and ferns as an informal grouping, such as the International Association of Pteridologists and the Pteridophyte Phylogeny Group.
|Plant growth and habit|
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