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
Myoxanthus octomeriae is a species of orchid occurring from Mexico to Guyana.'Myoxanthus octomeriae' at the Encyclopedia of Life'Myoxanthus octomerioides' at the Encyclopedia of Life
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
Asparagales is an order of plants in modern classification systems such as the Angiosperm Phylogeny Group and the Angiosperm Phylogeny Web. The order takes its name from the type family Asparagaceae and is placed in the monocots amongst the lilioid monocots; the order has only been recognized in classification systems. It was first put forward by Huber in 1977 and taken up in the Dahlgren system of 1985 and the APG in 1998, 2003 and 2009. Before this, many of its families were assigned to the old order Liliales, a large order containing all monocots with colourful tepals and lacking starch in their endosperm. DNA sequence analysis indicated that many of the taxa included in Liliales should be redistributed over three orders, Liliales and Dioscoreales; the boundaries of the Asparagales and of its families have undergone a series of changes in recent years. In the APG circumscription, Asparagales is the largest order of monocots with 14 families, 1,122 genera, about 36,000 species; the order is circumscribed on the basis of molecular phylogenetics, but is difficult to define morphologically, since its members are structurally diverse.
Most species of Asparagales are herbaceous perennials, although some are climbers and some are tree-like. The order contains many geophytes. According to telomere sequence, at least two evolutionary switch-points happened within the order. Basal sequence is formed by TTTAGGG like in majority of higher plants. Basal motif was changed to vertebrate-like TTAGGG and the most divergent motif CTCGGTTATGGG appears in Allium. One of the defining characteristics of the order is the presence of phytomelanin, a black pigment present in the seed coat, creating a dark crust. Phytomelanin is found in most families of the Asparagales; the leaves of all species form a tight rosette, either at the base of the plant or at the end of the stem, but along the stem. The flowers are not distinctive, being'lily type', with six tepals and up to six stamina; the order is thought to have first diverged from other related monocots some 120–130 million years ago, although given the difficulty in classifying the families involved, estimates are to be uncertain.
From an economic point of view, the order Asparagales is second in importance within the monocots to the order Poales. Species are used as food and flavourings, as cut flowers, as garden ornamentals. Although most species in the order are herbaceous, some no more than 15 cm high, there are a number of climbers, as well as several genera forming trees, which can exceed 10 m in height. Succulent genera occur in several families. All species have a tight cluster of leaves, either at the base of the plant or at the end of a more-or-less woody stem as with Yucca. In some cases the leaves are produced along the stem; the flowers are in the main not distinctive, being of a general'lily type', with six tepals, either free or fused from the base and up to six stamina. They are clustered at the end of the plant stem; the Asparagales are distinguished from the Liliales by the lack of markings on the tepals, the presence of septal nectaries in the ovaries, rather than the bases of the tepals or stamen filaments, the presence of secondary growth.
They are geophytes, but with linear leaves, a lack of fine reticular venation. The seeds characteristically have the external epidermis either obliterated, or if present, have a layer of black carbonaceous phytomelanin in species with dry fruits; the inner part of the seed coat is collapsed, in contrast to Liliales whose seeds have a well developed outer epidermis, lack phytomelanin, display a cellular inner layer. The orders which have been separated from the old Liliales are difficult to characterize. No single morphological character appears to be diagnostic of the order Asparagales; the flowers of Asparagales are of a general type among the lilioid monocots. Compared to Liliales, they have plain tepals without markings in the form of dots. If nectaries are present, they are in the septa of the ovaries rather than at the base of the tepals or stamens; those species which have large dry seeds have a dark, crust-like outer layer containing the pigment phytomelan. However, some species with hairy seeds, berries, or reduced seeds lack this dark pigment in their seed coats.
Phytomelan is not unique to Asparagales but it is common within the order and rare outside it. The inner portion of the seed coat is completely collapsed. In contrast, the morphologically similar seeds of Liliales have no phytomelan, retain a cellular structure in the inner portion of the seed coat. Most monocots are unable to thicken their stems once they have formed, since they lack the cylindrical meristem present in other angiosperm groups. Asparagales have a method of secondary thickening, otherwise only found inDioscorea. In a process called'anomalous secondary growth', they are able to create new
The Orchidaceae are a diverse and widespread family of flowering plants, with blooms that are colourful and fragrant known as the orchid family. Along with the Asteraceae, they are one of the two largest families of flowering plants; the Orchidaceae have about 28,000 accepted species, distributed in about 763 genera. The determination of which family is larger is still under debate, because verified data on the members of such enormous families are continually in flux. Regardless, the number of orchid species nearly equals the number of bony fishes and is more than twice the number of bird species, about four times the number of mammal species; the family encompasses about 6–11% of all seed plants. The largest genera are Bulbophyllum, Epidendrum and Pleurothallis, it includes Vanilla–the genus of the vanilla plant, the type genus Orchis, many cultivated plants such as Phalaenopsis and Cattleya. Moreover, since the introduction of tropical species into cultivation in the 19th century, horticulturists have produced more than 100,000 hybrids and cultivars.
Orchids are distinguished from other plants, as they share some evident, shared derived characteristics, or synapomorphies. Among these are: bilateral symmetry of the flower, many resupinate flowers, a nearly always modified petal, fused stamens and carpels, small seeds. All orchids are perennial herbs, they can grow according to two patterns: Monopodial: The stem grows from a single bud, leaves are added from the apex each year and the stem grows longer accordingly. The stem of orchids with a monopodial growth can reach several metres in length, as in Vanda and Vanilla. Sympodial: Sympodial orchids have a front and a back; the plant produces a series of adjacent shoots, which grow to a certain size and stop growing and are replaced. Sympodial orchids grow laterally following the surface of their support; the growth continues by development of new leads, with their own leaves and roots, sprouting from or next to those of the previous year, as in Cattleya. While a new lead is developing, the rhizome may start its growth again from a so-called'eye', an undeveloped bud, thereby branching.
Sympodial orchids may have visible pseudobulbs joined by a rhizome, which creeps along the top or just beneath the soil. Terrestrial orchids may form corms or tubers; the root caps of terrestrial orchids are white. Some sympodial terrestrial orchids, such as Orchis and Ophrys, have two subterranean tuberous roots. One is used as a food reserve for wintry periods, provides for the development of the other one, from which visible growth develops. In warm and humid climates, many terrestrial orchids do not need pseudobulbs. Epiphytic orchids, those that grow upon a support, have modified aerial roots that can sometimes be a few meters long. In the older parts of the roots, a modified spongy epidermis, called velamen, has the function of absorbing humidity, it can have a silvery-grey, white or brown appearance. In some orchids, the velamen includes spongy and fibrous bodies near the passage cells, called tilosomes; the cells of the root epidermis grow at a right angle to the axis of the root to allow them to get a firm grasp on their support.
Nutrients for epiphytic orchids come from mineral dust, organic detritus, animal droppings and other substances collecting among on their supporting surfaces. The base of the stem of sympodial epiphytes, or in some species the entire stem, may be thickened to form a pseudobulb that contains nutrients and water for drier periods; the pseudobulb has a smooth surface with lengthwise grooves, can have different shapes conical or oblong. Its size is variable; some Dendrobium species have long, canelike pseudobulbs with short, rounded leaves over the whole length. With ageing, the pseudobulb becomes dormant. At this stage, it is called a backbulb. Backbulbs still hold nutrition for the plant, but a pseudobulb takes over, exploiting the last reserves accumulated in the backbulb, which dies off, too. A pseudobulb lives for about five years. Orchids without noticeable pseudobulbs are said to have growths, an individual component of a sympodial plant. Like most monocots, orchids have simple leaves with parallel veins, although some Vanilloideae have reticulate venation.
Leaves may be ovate, lanceolate, or orbiculate, variable in size on the individual plant. Their characteristics are diagnostic, they are alternate on the stem folded lengthwise along the centre, have no stipules. Orchid leaves have siliceous bodies called stegmata in the vascular bundle sheaths and are fibrous; the structure of the leaves corresponds to the specific habitat of the plant. Species that bask in sunlight, or grow on sites which can be very dry, have thick, leathery leaves and the laminae are covered by a waxy cuticle to retain their necessary water supply. Shade-loving species, on the other hand, have thin leaves; the leaves of most orchids are perennial, that is, they live for several years, while others those with plicate leaves as in Catasetum, shed them annually and de
Myoxanthus lonchophyllus is a species of orchid endemic to southeastern Brazil. It is found in the Mantiqueira Rain Forest Mountains of Minas Gerais Brazil at elevations of 1000 to 1500 meters. Myoxanthus lonchophyllus at the Encyclopedia of Life
The Pleurothallidinae are a neotropical subtribe of plants of the orchid family including 29 genera in more than 4000 species. Occurring species of this subtribe are among the more popular orchids of horticulturalists the genera Dracula, Dryadella and Restrepia; the following genera are considered monophyletic: Barbosella, Dresslerella, Lepanthes, Platystele, Restrepia, Scaphosepalum and Zootrophion. Many genera in the Pleurothallidinae were found polyphyletic, for example species attributed to the genus Pleurothallis are scattered across five clades. Acianthera – Anathallis – Andinia – Barbosella – Brachionidium – Chamelophyton – Dilomilis – Diodonopsis – Draconanthes – Dracula – Dresslerella – Dryadella – Echinosepala – Frondaria – Kraenzlinella – Lepanthes – Lepanthopsis – Masdevallia – Myoxanthus – Neocogniauxia – Octomeria – Pabstiella – Phloeophila – Platystele – Pleurothallis – Pleurothallopsis – Porroglossum – Restrepia – Restrepiella – Scaphosepalum – Specklinia – Stelis – Teagueia – Tomzanonia – Trichosalpinx – Trisetella – Zootrophion DNA-based reclassification of the Pleurothallidinae Alec M. Pridgeon, Rodolfo Solano and Mark W. Chase - Phylogenetic relationships in Pleurothallidinae: combined evidence from nuclear and plastid DNA sequences.