In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring by sexual reproduction. Other ways of defining species include their karyotype, DNA sequence, behaviour or ecological niche. In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined. While these definitions may seem adequate, when looked at more they represent problematic species concepts. For example, the boundaries between related species become unclear with hybridisation, in a species complex of hundreds of similar microspecies, in a ring species. Among organisms that reproduce only asexually, the concept of a reproductive species breaks down, each clone is a microspecies. All species are given a two-part name, a "binomial"; the first part of a binomial is the genus.
The second part is called the specific epithet. For example, Boa constrictor is one of four species of the genus Boa. None of these is satisfactory definitions, but scientists and conservationists need a species definition which allows them to work, regardless of the theoretical difficulties. If species were fixed and distinct from one another, there would be no problem, but evolutionary processes cause species to change continually, to grade into one another. Species were seen from the time of Aristotle until the 18th century as fixed kinds that could be arranged in a hierarchy, the great chain of being. In the 19th century, biologists grasped. Charles Darwin's 1859 book The Origin of Species explained how species could arise by natural selection; that understanding was extended in the 20th century through genetics and population ecology. Genetic variability arises from mutations and recombination, while organisms themselves are mobile, leading to geographical isolation and genetic drift with varying selection pressures.
Genes can sometimes be exchanged between species by horizontal gene transfer. Viruses are a special case, driven by a balance of mutation and selection, can be treated as quasispecies. Biologists and taxonomists have made many attempts to define species, beginning from morphology and moving towards genetics. Early taxonomists such as Linnaeus had no option but to describe what they saw: this was formalised as the typological or morphological species concept. Ernst Mayr emphasised reproductive isolation, but this, like other species concepts, is hard or impossible to test. Biologists have tried to refine Mayr's definition with the recognition and cohesion concepts, among others. Many of the concepts are quite similar or overlap, so they are not easy to count: the biologist R. L. Mayden recorded about 24 concepts, the philosopher of science John Wilkins counted 26. Wilkins further grouped the species concepts into seven basic kinds of concepts: agamospecies for asexual organisms biospecies for reproductively isolated sexual organisms ecospecies based on ecological niches evolutionary species based on lineage genetic species based on gene pool morphospecies based on form or phenotype and taxonomic species, a species as determined by a taxonomist.
A typological species is a group of organisms in which individuals conform to certain fixed properties, so that pre-literate people recognise the same taxon as do modern taxonomists. The clusters of variations or phenotypes within specimens would differentiate the species; this method was used as a "classical" method of determining species, such as with Linnaeus early in evolutionary theory. However, different phenotypes are not different species. Species named in this manner are called morphospecies. In the 1970s, Robert R. Sokal, Theodore J. Crovello and Peter Sneath proposed a variation on this, a phenetic species, defined as a set of organisms with a similar phenotype to each other, but a different phenotype from other sets of organisms, it differs from the morphological species concept in including a numerical measure of distance or similarity to cluster entities based on multivariate comparisons of a reasonably large number of phenotypic traits. A mate-recognition species is a group of sexually reproducing organisms that recognize one another as potential mates.
Expanding on this to allow for post-mating isolation, a cohesion species is the most inclusive population of individuals having the potential for phenotypic cohesion through intrinsic cohesion mechanisms. A further development of the recognition concept is provided by the biosemiotic concept of species. In microbiology, genes can move even between distantly related bacteria extending to the whole bacterial domain; as a rule of thumb, microbiologists have assumed that kinds of Bacteria or Archaea with 16S ribosomal RNA gene sequences more similar than 97% to each other need to be checked by DNA-DNA hybridisation to decide if they belong to the same species or not. This concept was narrowed in 2006 to a similarity of 98.7%. DNA-DNA hybri
The flowering plants known as angiosperms, Angiospermae or Magnoliophyta, are the most diverse group of land plants, with 64 orders, 416 families 13,164 known genera and c. 369,000 known species. Like gymnosperms, angiosperms are seed-producing plants. However, they are distinguished from gymnosperms by characteristics including flowers, endosperm within the seeds, the production of fruits that contain the seeds. Etymologically, angiosperm means a plant; the term comes from the Greek words sperma. The ancestors of flowering plants diverged from gymnosperms in the Triassic Period, 245 to 202 million years ago, the first flowering plants are known from 160 mya, they diversified extensively during the Early Cretaceous, became widespread by 120 mya, replaced conifers as the dominant trees from 100 to 60 mya. Angiosperms differ from other seed plants in several ways, described in the table below; these distinguishing characteristics taken together have made the angiosperms the most diverse and numerous land plants and the most commercially important group to humans.
Angiosperm stems are made up of seven layers. The amount and complexity of tissue-formation in flowering plants exceeds that of gymnosperms; the vascular bundles of the stem are arranged such that the phloem form concentric rings. In the dicotyledons, the bundles in the young stem are arranged in an open ring, separating a central pith from an outer cortex. In each bundle, separating the xylem and phloem, is a layer of meristem or active formative tissue known as cambium. By the formation of a layer of cambium between the bundles, a complete ring is formed, a regular periodical increase in thickness results from the development of xylem on the inside and phloem on the outside; the soft phloem becomes crushed, but the hard wood persists and forms the bulk of the stem and branches of the woody perennial. Owing to differences in the character of the elements produced at the beginning and end of the season, the wood is marked out in transverse section into concentric rings, one for each season of growth, called annual rings.
Among the monocotyledons, the bundles are more numerous in the young stem and are scattered through the ground tissue. They once formed the stem increases in diameter only in exceptional cases; the characteristic feature of angiosperms is the flower. Flowers show remarkable variation in form and elaboration, provide the most trustworthy external characteristics for establishing relationships among angiosperm species; the function of the flower is to ensure fertilization of the ovule and development of fruit containing seeds. The floral apparatus may arise terminally from the axil of a leaf; as in violets, a flower arises singly in the axil of an ordinary foliage-leaf. More the flower-bearing portion of the plant is distinguished from the foliage-bearing or vegetative portion, forms a more or less elaborate branch-system called an inflorescence. There are two kinds of reproductive cells produced by flowers. Microspores, which will divide to become pollen grains, are the "male" cells and are borne in the stamens.
The "female" cells called megaspores, which will divide to become the egg cell, are contained in the ovule and enclosed in the carpel. The flower may consist only of these parts, as in willow, where each flower comprises only a few stamens or two carpels. Other structures are present and serve to protect the sporophylls and to form an envelope attractive to pollinators; the individual members of these surrounding structures are known as petals. The outer series is green and leaf-like, functions to protect the rest of the flower the bud; the inner series is, in general, white or brightly colored, is more delicate in structure. It functions to attract bird pollinators. Attraction is effected by color and nectar, which may be secreted in some part of the flower; the characteristics that attract pollinators account for the popularity of flowers and flowering plants among humans. While the majority of flowers are perfect or hermaphrodite, flowering plants have developed numerous morphological and physiological mechanisms to reduce or prevent self-fertilization.
Heteromorphic flowers have short carpels and long stamens, or vice versa, so animal pollinators cannot transfer pollen to the pistil. Homomorphic flowers may employ a biochemical mechanism called self-incompatibility to discriminate between self and non-self pollen grains. In other species, the male and female parts are morphologically separated, developing on different flowers; the botanical term "Angiosperm", from the Ancient Greek αγγείον, angeíon and σπέρμα, was coined in the form Angiospermae by Paul Hermann in 1690, as the name of one of his primary divisions of the plant kingdom. This included flowering plants possessing seeds enclosed in capsules, distinguished from his Gymnospermae, or flowering plants with achenial or schizo-carpic fruits, the whole fruit or each of its pieces being here regarded as a seed and naked; the term and its antonym were maintained by Carl Linnaeus with the same sense, but with restricted application, in the names of the orders of his class Didynamia. Its use with any
Monocotyledons referred to as monocots, are flowering plants whose seeds contain only one embryonic leaf, or cotyledon. They constitute one of the major groups into which the flowering plants have traditionally been divided, the rest of the flowering plants having two cotyledons and therefore classified as dicotyledons, or dicots. However, molecular phylogenetic research has shown that while the monocots form a monophyletic group or clade, the dicots do not. Monocots have always been recognized as a group, but with various taxonomic ranks and under several different names; the APG III system of 2009 recognises a clade called "monocots" but does not assign it to a taxonomic rank. The monocots include about 60,000 species; the largest family in this group by number of species are the orchids, with more than 20,000 species. About half as many species belong to the true grasses, which are economically the most important family of monocots. In agriculture the majority of the biomass produced; these include not only major grains, but forage grasses, sugar cane, the bamboos.
Other economically important monocot crops include various palms and plantains, gingers and their relatives and cardamom, pineapple, water chestnut, leeks and garlic. Many houseplants are monocot epiphytes. Additionally most of the horticultural bulbs, plants cultivated for their blooms, such as lilies, irises, cannas and tulips, are monocots; the monocots or monocotyledons have, as the name implies, a single cotyledon, or embryonic leaf, in their seeds. This feature was used to contrast the monocots with the dicotyledons or dicots which have two cotyledons. From a diagnostic point of view the number of cotyledons is neither a useful characteristic, nor is it reliable; the single cotyledon is only one of a number of modifications of the body plan of the ancestral monocotyledons, whose adaptive advantages are poorly understood, but may have been related to adaption to aquatic habitats, prior to radiation to terrestrial habitats. Monocots are sufficiently distinctive that there has been disagreement as to membership of this group, despite considerable diversity in terms of external morphology.
However, morphological features that reliably characterise major clades are rare. Thus monocots are distinguishable from other angiosperms both in terms of their uniformity and diversity. On the one hand the organisation of the shoots, leaf structure and floral configuration are more uniform than in the remaining angiosperms, yet within these constraints a wealth of diversity exists, indicating a high degree of evolutionary success. Monocot diversity includes perennial geophytes such as ornamental flowers including and succulent epiphytes, all in the lilioid monocots, major cereal grains in the grass family and forage grasses as well as woody tree-like palm trees, bamboo and bromeliads, bananas and ginger in the commelinid monocots, as well as both emergent and aroids, as well as floating or submerged aquatic plants such as seagrass. Organisation and life formsThe most important distinction is their growth pattern, lacking a lateral meristem that allows for continual growth in diameter with height, therefore this characteristic is a basic limitation in shoot construction.
Although herbaceous, some arboraceous monocots reach great height and mass. The latter include agaves, palms and bamboos; this creates challenges in water transport. Some, such as species of Yucca, develop anomalous secondary growth, while palm trees utilise an anomalous primary growth form described as establishment growth; the axis undergoes primary thickening, that progresses from internode to internode, resulting in a typical inverted conical shape of the basal primary axis. The limited conductivity contributes to limited branching of the stems. Despite these limitations a wide variety of adaptive growth forms has resulted from epiphytic orchids and bromeliads to submarine Alismatales and mycotrophic Burmanniaceae and Triuridaceae. Other forms of adaptation include the climbing vines of Araceae which use negative phototropism to locate host trees, while some palms such as Calamus manan produce the longest shoots in the plant kingdom, up to 185 m long. Other monocots Poales, have adopted a therophyte life form.
LeavesThe cotyledon, the primordial Angiosperm leaf consists of a proximal leaf base or hypophyll and a distal hyperphyll. In monocots the hypophyll tends to be the dominant part in contrast to other angiosperms. From these, considerable diversity arises. Mature monocot leaves are narrow and linear, forming a sheath
The tribe Epidendreae of the Orchidaceae comprises six subtribes: Bletiinae sensu MMIV, which contains only the genera Basiphyllaea and Hexalectris Chysinae Coeliinae Laeliinae Pleurothallidinae Ponerinae
In biology, a hybrid is the offspring resulting from combining the qualities of two organisms of different breeds, species or genera through sexual reproduction. Hybrids are not always intermediates between their parents, but can show hybrid vigour, sometimes growing larger or taller than either parent; the concept of a hybrid is interpreted differently in animal and plant breeding, where there is interest in the individual parentage. In genetics, attention is focused on the numbers of chromosomes. In taxonomy, a key question is how related the parent species are. Species are reproductively isolated by strong barriers to hybridisation, which include morphological differences, differing times of fertility, mating behaviors and cues, physiological rejection of sperm cells or the developing embryo; some act before fertilization and others after it. Similar barriers exist in plants, with differences in flowering times, pollen vectors, inhibition of pollen tube growth, somatoplastic sterility, cytoplasmic-genic male sterility and the structure of the chromosomes.
A few animal species and many plant species, are the result of hybrid speciation, including important crop plants such as wheat, where the number of chromosomes has been doubled. Human impact on the environment has resulted in an increase in the interbreeding between regional species, the proliferation of introduced species worldwide has resulted in an increase in hybridisation; this genetic mixing may threaten many species with extinction, while genetic erosion in crop plants may be damaging the gene pools of many species for future breeding. A form of intentional human-mediated hybridisation is the crossing of wild and domesticated species; this is common in modern agriculture. One such flower, Oenothera lamarckiana, was central to early genetics research into mutationism and polyploidy, it is more done in the livestock and pet trades. Human selective breeding of domesticated animals and plants has resulted is the development of distinct breeds. Hybrid humans existed in prehistory. For example and anatomically modern humans are thought to have interbred as as 40,000 years ago.
Mythological hybrids appear in human culture in forms as diverse as the Minotaur, blends of animals and mythical beasts such as centaurs and sphinxes, the Nephilim of the Biblical apocrypha described as the wicked sons of fallen angels and attractive women. The term hybrid is derived from Latin hybrida, used for crosses such as of a tame sow and a wild boar; the term came into popular use in English in the 19th century, though examples of its use have been found from the early 17th century. Conspicuous hybrids are popularly named with portmanteau words, starting in the 1920s with the breeding of tiger–lion hybrids. From the point of view of animal and plant breeders, there are several kinds of hybrid formed from crosses within a species, such as between different breeds. Single cross hybrids result from the cross between two true-breeding organisms which produces an F1 hybrid; the cross between two different homozygous lines produces an F1 hybrid, heterozygous. The F1 generation is phenotypically homogeneous, producing offspring that are all similar to each other.
Double cross hybrids result from the cross between two different F1 hybrids. Three-way cross hybrids result from the cross between an inbred line. Triple cross hybrids result from the crossing of two different three-way cross hybrids. Top cross hybrids result from the crossing of a top quality or pure-bred male and a lower quality female, intended to improve the quality of the offspring, on average. Population hybrids result from the crossing of plants or animals in one population with those of another population; these crosses between different breeds. In horticulture, the term stable hybrid is used to describe an annual plant that, if grown and bred in a small monoculture free of external pollen produces offspring that are "true to type" with respect to phenotype. Hybridisation can occur in the hybrid zones where the geographical ranges of species, subspecies, or distinct genetic lineages overlap. For example, the butterfly Limenitis arthemis has two major subspecies in North America, L. a. arthemis and L. a. astyanax.
The white admiral has a bright, white band on its wings, while the red-spotted purple has cooler blue-green shades. Hybridisation occurs between a narrow area across New England, southern Ontario, the Great Lakes, the "suture region", it is at these regions. Other hybrid zones have formed between described species of animals. From the point of view of genetics, several different kinds of hybrid can be distinguished. A genetic hybrid carries two different alleles of the same gene, where for instance one allele may code for a lighter coat colour than the other. A structural hybrid results from the fusion of gametes that have differing structure in at least one chromosome, as a result of structural abnormalities. A numerical hybrid results from the fusion of gamet
Laeliinae is a Neotropical subtribe including 40 orchid genera, such as Brassavola and Cattleya. The genus Epidendrum is the largest within this subtribe; this is followed with over 120 species. Genus and Number of Species: Acrorchis Dressler, 1 Adamantinia Van den Berg & M. W. Chase, 1 Alamania La Llave & Lex. 1 Arpophyllum La Llave & Lex, 5 Artorima Dressler & G. E. Pollard, 1 Barkeria Knowles & Westc. 17 Syn. Dothilophis Raf. Brassavola R. Br. 17 Broughtonia R. Br. 6 Syn. Cattleyopsis Lem. Laeliopsis Lindl. Cattleya Lindl. 118 Syn. Maelenia Dum. Sophronitis Lindl. Sophronia Lindl. Lophoglottis Raf. Hoffmannseggella H. G. Jones, Hadrolaelia Chiron & V. P. Castro, Dungsia Chiron & V. P. Castro, Microlaelia Chiron & V. P. Castro, Chironiella Braem, Brasilaelia Campacci, Cattleyella Van den Berg & M. W. Chase, Schluckebieria Braem Caularthron Raf. 3 Syn. Diacrium Benth. Dothilophis Raf. Constantia Barb. Rodr. 5 Dimerandra Schltr. 1 Dinema Lindl. 1 Domingoa Schltr. 5 Syn. Hartwegia Lindl. Nageliella L. O. Williams Encyclia Hook. 120 Epidendrum L. 1500 Syn.
Amblostoma Scheidw. Amblystoma Kuntze, Amphiglottis Salisb. Amphiglottium Lindl. Ex Stein, Auliza Salisb. Auliza Salisb. Ex Small, Aulizeum Lindl. Ex Stein, Coilostylis Raf. Didothion Raf. Diothonea Lindl. Epidanthus L. O. Williams, Epidendropsis Garay & Dunst. Gastropodium Lindl. Hemiscleria Lindl. Kalopternix Garay & Dunst. Lanium Benth. Larnandra Raf. Minicolumna Brieger, Nanodes Lindl. Neohlemannia Kraenzl. Neowilliamsia Garay, Nyctosma Raf. Oerstedella Rchb.f. Physinga Lindl. Pleuranthium Benth. Pseudepidendrum Rchb.f. Psilanthemum Klotszch ex Stein, Seraphyta Fisch. & C. A. Mey. Spathiger Small, Spathium Lindl. Ex Stein, Stenoglossum Kunth, Tritelandra Raf. Guarianthe Dressler & W. E. Higgins, 4 Hagsatera R. González, 2 Homalopetalum Rolfe, 7 Syn. Pinelia Lindl. Pinelianthe Rauschert Isabelia Barb. Rodr. 3 Syn. Neolauchea Kraenzl. Sophronitella Schltr. Jacquiniella Schltr. 11 Syn. Dressleriella Brieger, Briegeria Senghas Laelia Lindl. 25 Syn. Amalia Lindl. Amalias Hofmsgg. Schomburgkia Lindl. Laeliocatarthron Leptotes Lindl. 5 Loefgrenianthus Hoehne, 1 Meiracyllium Rchb.f.
2 Microepidendrum Brieger ex W. E. Higgins, 1 Myrmecophila Rolfe, 10 Nidema Britton & Millsp. 2 Oestlundia W. E. Higgins, 4 Orleanesia Barb. Rodr. 11 Prosthechea Knowles & Westc. 100 Syn. Epithecium Knowles & Westc. Hormidium Heynh. Anacheilium Hoffmgg. Euchile Withner, Pseudencyclia Chiron & V. P. Castro. Panarica Withner & P. A. Harding, Pollardia Withner & P. A. Harding Pseudolaelia Porto & Brade, 10 Syn. Renata Ruschi Psychilis Raf. 15 Pygmaeorchis Brade, 2 Quisqueya Dod, 4 Rhyncholaelia Schltr, 2 Scaphyglottis Poepp. & Endl. 60 Syn. Hexisea Lindl. Cladobium Lindl. Hexadesmia Brongn. Tetragamestus Rchb.f. Reichenbachanthus Barb. Rodr. Fractiungis Schltr. Leaoa Schltr. & Porto, Pachystele Schltr. Costaricaea Schltr. Ramonia Schltr. Platyglottis L. O. Williams Tetramicra Lindl. 13 van den Berg, C. W. E. Higgins, R. L. Dressler, W. M. Whitten, M. A. Soto Arenas, A. Culham and M. W. Chase. 2000. A Phylogenetic Analysis of Laeliinae Based on Sequence Data from Internal Transcribed Spacers of Nuclear Ribosomal DNA. Lindleyana 15: 96–114.
Van den Berg, C. et al. 2005. Subtribe Laeliinae. Pp. 181–316 In Pridgeon, A. M. Cribb, P. J. Chase, M. W. Rasmussen, F. N. Genera Orchidacearum Vol. IV. Oxford University Press, Oxford. Van den Berg C, Chase M. W. 2005 Nomenclatural notes on Laeliinae - IV. New combinations in Sophronitis. Kew Bull. 59.: 565-567 van den Berg, C. 2014. Reaching a compromise between conflicting nuclear and plastid phylogenetic trees: a new classification for the genus Cattleya. Phytotaxa 186: 075–086. Photo album of Laeliinae species and hybrids Checklist of Laeliinae genera
In plant systematics Epidendroideae is a subfamily of the orchid family, Orchidaceae. Epidendroideae is larger than all the other orchid subfamilies together, comprising more than 15,000 species in 576 genera. Most Epidendroid orchids are tropical epiphytes with pseudobulbs. There are, some terrestrials such as Epipactis and a few myco-heterotrophs, which are parasitic upon mycorrhizal fungi, they contain the remaining orchids with a single, fertile anther, fully incumbent to suberect. The anther form arises from early anther bending; the incumbent anther is pointed backward in many genera. Most have hard pollinia, i.e. a mass of waxy pollen or of coherent pollen grains. The pollinia are without; the stigma are three-lobed. The apical part of the middle stigma lobe forms a stipe; the ovary is unilocular. The leaves are distichous or spiraling; the Epidendroideae are difficult to classify. They have been divided in “lower epidendroids” and “higher epidendroids”. Epiphytes are plants which grow on top of other plants.
They are not parasitic. By growing on other plants, the epiphytes can reach to the light better or where they can avoid struggling for light. Many mosses and lichens are epiphytes, as are 10 per cent of all seed plants and ferns. Epiphytes are common in some groups of plants, such as ferns, mosses and algae. Over half of the 20,000 species of orchids are epiphytes. Most epiphytic seed plants and ferns are found in tropical and subtropical rainforests because they need high humidity to survive; the areas which most epiphytes grow are the montane rainforests. Epiphytic orchids are found on many positions of the host tree, depending on species requirements and size, some large species will grow in a fork, whereas some small species scramble through thin branches, other species will climb up the trunk etc. etc. The trees provide many habitats with different conditions of temperature and light. In temperate places, epiphytes are most common in moist forests, such as the rainforests in Queensland. Epiphytes are not adapted to droughts in the same way are other flora, because they don’t have access to the ground, but they still have some mechanisms to help them survive.
Some become dormant for months at a time. They contain absorptive plants that are capable at taking up water when it is available and preventing drought when water is scarcer. CAM can be impeded by higher night-time temperatures, dehydrated tissues, high saturation deficits in the surrounding air, which lower the "stomata conductance" of the epiphytes, reducing the CO2 uptake, which in turn reduces growth and reproduction and induces carbon loss. Higher temperatures, strain on evaporation, contact to light cause CAM-idling, the epiphyte closing its stomata when it becomes stressed, that brings down the range of habitats a species can inhabit. Epiphyte species work biomasses are much more sensitive to different relative moisture levels than other plants; the Epidendroideae subfamily is divided into two clades or subgroups known as the higher epidendroids and the lower epidendroids. The higher epidendroids are monophyletic and polyphyletic; the tribes are listed below: This classification has a rather ephemeral nature and is prone to frequent revision.
Changes are to occur as new morphological and genetic data become available. A phylogenetic analysis of the Orchidaceae - evidence from rbcL nucleotide sequences Orchid Tree: a phylogeny of epiphytes on the tree of life