Fern ally
Fern allies are a diverse group of seedless vascular plants that are not true ferns. Like ferns, a fern ally disperses by shedding spores to initiate an alternation of generations. Three or four groups of plants were considered to be fern allies. In various classification schemes, these may be grouped as classes or divisions within the plant kingdom. Fern allies and ferns were sometimes grouped together as division Pteridophyta. Another traditional classification scheme of living plants is as follows: Kingdom: Plantae Division Tracheophyta Class Lycopsida and related plants Class Sphenopsida or Equisetopsida and scouring-rushes Class Psilopsida, whisk ferns Class Filices or Pteropsida, true ferns Class Spermatopsida More recent evidence shows that the class Filices, as described above, is not monophyletic; the following classification represents a consensus view: Kingdom PlantaeSubkingdom Tracheobionta Division Lycopodiophyta Class Lycopodiopsida, clubmosses Class Selaginellopsida, spikemosses Class Isoetopsida and scale trees Division Pteridophyta Class Equisetopsida and scouring-rushes Class Psilotopsida, whisk ferns, adders'-tongues and moonworts Class Marattiopsida, marattioid ferns Class Pteridopsida, leptosporangiate ferns Division Spermatophyta Note that in either scheme, the same basic groups are recognized, but in the most recent scheme only the Lycopodiophyta is not classified with the ferns.
Another way of looking at this relationship is. Several groups of plants were considered "fern allies": the clubmosses and quillworts in the Lycopodiophyta, the whisk ferns in Psilotaceae, the horsetails in the Equisetaceae. Traditionally, three discrete groups of plants had been considered ferns: the adders-tongues and grape-ferns, the Marattiaceae, the leptosporangiate ferns. More recent genetic studies have shown that the Lycopodiophyta are only distantly related to any other vascular plants, having radiated evolutionarily at the base of the vascular plant clade, while both the whisk ferns and horsetails are as much true ferns as are the Ophioglossoids and Marattiaceae; the Marattiaceae are a group of tropical ferns with a large, fleshy rhizome, are now thought to be a sister group to the main group of ferns, the leptosporangiate ferns. The whisk ferns and Ophioglossids are demonstrably a clade, the relationships between these this group, the leptosporangiate ferns+marattiaceae, the horsetails remains uncertain.
Common Ferns and Fern-Ally Species A Classification of the Ferns and Fern-Allies Non-seed plant images at bioimages.vanderbilt.edu Lord, Thomas R.. Ferns and Fern Allies of Pennsylvania. Indiana, PA: Pinelands Press
Equisetaceae
Equisetaceae, sometimes called the horsetail family, is the only extant family of the order Equisetales, with one surviving genus, which comprises about twenty species. Equisetaceae is the only surviving family of the Equisetales, a group with many fossils of large tree-like plants that possessed ribbed stems similar to modern horsetails. Pseudobornia is the oldest known relative of Equisetum. All living horsetails are placed in the genus Equisetum, but there are some fossil species. Equisetites is a "wastebin taxon" uniting all sorts of large horsetails from the Mesozoic, but while some of the species placed there are to be ancestral to the modern horsetails, there have been reports of secondary growth in other Equisetites, these represent a distinct and now-extinct horsetail lineage. Equicalastrobus is the name given to fossil horsetail strobili, which mostly or belong to the plants placed in Equisetites. UCMP – Equisetaceae
Monophyly
In cladistics, a monophyletic group, or clade, is a group of organisms that consists of all the descendants of a common ancestor. Monophyletic groups are characterised by shared derived characteristics, which distinguish organisms in the clade from other organisms; the arrangement of the members of a monophyletic group is called a monophyly. Monophyly is contrasted with polyphyly as shown in the second diagram. A paraphyletic group consists of all of the descendants of a common ancestor minus one or more monophyletic groups. A polyphyletic group is characterized by convergent habits of scientific interest; the features by which a polyphyletic group is differentiated from others are not inherited from a common ancestor. These definitions have taken some time to be accepted; when the cladistics school of thought became mainstream in the 1960s, several alternative definitions were in use. Indeed, taxonomists sometimes used terms without defining them, leading to confusion in the early literature, a confusion which persists.
The first diagram shows a phylogenetic tree with two monophyletic groups. The several groups and subgroups are situated as branches of the tree to indicate ordered lineal relationships between all the organisms shown. Further, any group may be considered a taxon by modern systematics, depending upon the selection of its members in relation to their common ancestor; the term monophyly, or monophyletic, derives from the two Ancient Greek words μόνος, meaning "alone, unique", φῦλον, meaning "genus, species", refers to the fact that a monophyletic group includes organisms consisting of all the descendants of a unique common ancestor. Conversely, the term polyphyly, or polyphyletic, builds on the ancient greek prefix πολύς, meaning "many, a lot of", refers to the fact that a polyphyletic group includes organisms arising from multiple ancestral sources. By comparison, the term paraphyly, or paraphyletic, uses the ancient greek prefix παρά, meaning "beside, near", refers to the situation in which one or several monophyletic subgroups are left apart from all other descendants of a unique common ancestor.
That is, a paraphyletic group is nearly monophyletic, hence the prefix pará. On the broadest scale, definitions fall into two groups. Willi Hennig defined monophyly as groups based on synapomorphy; some authors have sought to define monophyly to include paraphyly as any two or more groups sharing a common ancestor. However, this broader definition encompasses both monophyletic and paraphyletic groups as defined above. Therefore, most scientists today restrict the term "monophyletic" to refer to groups consisting of all the descendants of one common ancestor. However, when considering taxonomic groups such as genera and species, the most appropriate nature of their common ancestor is unclear. Assuming that it would be one individual or mating pair is unrealistic for sexually reproducing species, which are by definition interbreeding populations. Monophyly and associated terms are restricted to discussions of taxa, are not accurate when used to describe what Hennig called tokogenetic relationships—now referred to as genealogies.
Some argue that using a broader definition, such as a species and all its descendants, does not work to define a genus. The loose definition fails to recognize the relations of all organisms. According to D. M. Stamos, a satisfactory cladistic definition of a species or genus is impossible because many species may form by "budding" from an existing species, leaving the parent species paraphyletic. Clade Crown group Glossary of scientific naming Monotypic taxon Paraphyly Polyphyly Abbey, Darren. "Graphical explanation of basic phylogenetic terms". University of California, Berkeley. Retrieved 15 January 2010. Carr, Steven M.. "Concepts of monophyly, polyphyly & paraphyly". Memorial University. Retrieved 15 January 2010. Hyvönen, Jaako. "Monophyly, compromise". University of Helsinki. Retrieved 15 January 2010
Phloem
In vascular plants, phloem is the living tissue that transports the soluble organic compounds made during photosynthesis and known as photosynthates, in particular the sugar sucrose, to parts of the plant where needed. This transport process is called translocation. In trees, the phloem is the innermost layer of the bark, hence the name, derived from the Greek word φλοιός meaning "bark"; the term was introduced by Nägeli in 1858. Phloem tissue consists of conducting cells called sieve elements, parenchyma cells, including both specialized companion cells or albuminous cells and unspecialized cells and supportive cells, such as fibres and sclereids. Sieve elements are the type of cell that are responsible for transporting sugars throughout the plant. At maturity they lack a nucleus and have few organelles, so they rely on companion cells or albuminous cells for most of their metabolic needs. Sieve tube cells do contain vacuoles and other organelles, such as ribosomes, before they mature, but these migrate to the cell wall and dissolve at maturity.
One of the few organelles they do contain at maturity is the rough endoplasmic reticulum, which can be found at the plasma membrane nearby the plasmodesmata that connect them to their companion or albuminous cells. All sieve cells have groups of pores at their ends that grow from modified and enlarged plasmodesmata, called sieve areas; the pores are reinforced by platelets of a polysaccharide called callose. They are of two types and chlorenchyma. Other parenchyma cells within the phloem are undifferentiated and used for food storage; the metabolic functioning of sieve-tube members depends on a close association with the companion cells, a specialized form of parenchyma cell. All of the cellular functions of a sieve-tube element are carried out by the companion cell, a typical nucleate plant cell except the companion cell has a larger number of ribosomes and mitochondria; the dense cytoplasm of a companion cell is connected to the sieve-tube element by plasmodesmata. The common sidewall shared by a sieve tube element and a companion cell has large numbers of plasmodesmata.
There are two types of companion cells. Ordinary companion cells, which have smooth walls and few or no plasmodesmatal connections to cells other than the sieve tube. Transfer cells, which have much-folded walls that are adjacent to non-sieve cells, allowing for larger areas of transfer, they are specialized in scavenging solutes from those in the cell walls that are pumped requiring energy. Albuminous cells have a similar role to companion cells, but are associated with sieve cells only and are hence found only in seedless vascular plants and gymnosperms. Although its primary function is transport of sugars, phloem may contain cells that have a mechanical support function; these fall into two categories: fibres and sclereids. Both cell types are therefore dead at maturity; the secondary cell wall increases their tensile strength. Bast fibres are the long, narrow supportive cells that provide tension strength without limiting flexibility, they are found in xylem, are the main component of many textiles such as paper and cotton.
Sclereids are irregularly shaped cells that add compression strength but may reduce flexibility to some extent. They serve as anti-herbivory structures, as their irregular shape and hardness will increase wear on teeth as the herbivores chews. For example, they are responsible for the gritty texture in pears, in winter bears Unlike xylem, the phloem is composed of still-living cells that transport sap; the sap is a water-based solution, but rich in sugars made by photosynthesis. These sugars are transported to non-photosynthetic parts of the plant, such as the roots, or into storage structures, such as tubers or bulbs. During the plant's growth period during the spring, storage organs such as the roots are sugar sources, the plant's many growing areas are sugar sinks; the movement in phloem is multidirectional. After the growth period, when the meristems are dormant, the leaves are sources, storage organs are sinks. Developing seed-bearing organs are always sinks; because of this multi-directional flow, coupled with the fact that sap cannot move with ease between adjacent sieve-tubes, it is not unusual for sap in adjacent sieve-tubes to be flowing in opposite directions.
While movement of water and minerals through the xylem is driven by negative pressures most of the time, movement through the phloem is driven by positive hydrostatic pressures. This process is termed translocation, is accomplished by a process called phloem loading and unloading. Phloem sap is thought to play a role in sending informational signals throughout vascular plants. "Loading and unloading patterns are determined by the conductivity and number of plasmodesmata and the position-dependent function of solute-specific, plasma membrane transport proteins. Recent evidence indicates that mobile proteins and RNA are part of the plant's long-distance communication signaling system. Evidence exists for the directed transport and sorting of macromolecules as they pass through plasmodesmata."Organic molecules such as sugars, amino acids, certain hormones, messenger RNAs are transported in the phloem through sieve tube elements. Because phloem tubes are located outside the xylem in most plants, a tree or other plant can be killed by stripping away the bark in a ring on the trunk or stem.
With the phloem destroyed, nutrients cannot reach the
Vascular tissue
Vascular tissue is a complex conducting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the phloem; these two tissues transport fluid and nutrients internally. There are two meristems associated with vascular tissue: the vascular cambium and the cork cambium. All the vascular tissues within a particular plant together constitute the vascular tissue system of that plant; the cells in vascular tissue are long and slender. Since the xylem and phloem function in the conduction of water and nutrients throughout the plant, it is not surprising that their form should be similar to pipes; the individual cells of phloem are connected end-to-end. As the plant grows, new vascular tissue differentiates in the growing tips of the plant; the new tissue is aligned with existing vascular tissue, maintaining its connection throughout the plant. The vascular tissue in plants is arranged in discrete strands called vascular bundles; these bundles include both phloem, as well as supporting and protective cells.
In stems and roots, the xylem lies closer to the interior of the stem with phloem towards the exterior of the stem. In the stems of some Asterales dicots, there may be phloem located inwardly from the xylem as well. Between the xylem and phloem is a meristem called the vascular cambium; this tissue divides off cells that will become additional phloem. This growth increases the girth of the plant, rather than its length; as long as the vascular cambium continues to produce new cells, the plant will continue to grow more stout. In trees and other plants that develop wood, the vascular cambium allows the expansion of vascular tissue that produces woody growth; because this growth ruptures the epidermis of the stem, woody plants have a cork cambium that develops among the phloem. The cork cambium gives rise to thickened cork cells to protect the surface of the plant and reduce water loss. Both the production of wood and the production of cork are forms of secondary growth. In leaves, the vascular bundles are located among the spongy mesophyll.
The xylem is oriented toward the adaxial surface of the leaf, phloem is oriented toward the abaxial surface of the leaf. This is why aphids are found on the undersides of the leaves rather than on the top, since the phloem transports sugars manufactured by the plant and they are closer to the lower surface. Xylem Phloem Cork cambium Vascular cambium Vascular plant Stele Circulatory system Intro to Plant Structure Contains diagrams of the plant tissues, listed as an outline
Fern
A fern is a member of a group of vascular plants that reproduce via spores and have neither seeds nor flowers. They differ from mosses by being vascular, i.e. having specialized tissues that conduct water and nutrients and in having life cycles in which the sporophyte is the dominant phase. Like other vascular plants, ferns have complex leaves called megaphylls, that are more complex than the microphylls of clubmosses. Most ferns are leptosporangiate ferns, sometimes referred to as true ferns, they produce coiled fiddleheads that expand into fronds. The group includes about 10,560 known extant species. Ferns are defined here in the broad sense, being all of the Polypodiopsida, comprising both the leptosporangiate and eusporangiate ferns, the latter itself comprising ferns other than those denominated true ferns, including horsetails or scouring rushes, whisk ferns, marattioid ferns, ophioglossoid ferns. Ferns first appear in the fossil record about 360 million years ago in the late Devonian period, but many of the current families and species did not appear until 145 million years ago in the early Cretaceous, after flowering plants came to dominate many environments.
The fern Osmunda claytoniana is a paramount example of evolutionary stasis. Ferns are not of major economic importance, but some are used for food, medicine, as biofertilizer, as ornamental plants and for remediating contaminated soil, they have been the subject of research for their ability to remove some chemical pollutants from the atmosphere. Some fern species, such as bracken and water fern are significant weeds world wide; some fern genera, such as Azolla can fix nitrogen and make a significant input to the nitrogen nutrition of rice paddies. They play certain roles in mythology and art. Like the sporophytes of seed plants, those of ferns consist of stems and roots. Stems: Fern stems are referred to as rhizomes though they grow underground only in some of the species. Epiphytic species and many of the terrestrial ones have above-ground creeping stolons, many groups have above-ground erect semi-woody trunks; these can reach up to 20 meters tall in a few species. Leaf: The green, photosynthetic part of the plant is technically a megaphyll and in ferns, it is referred to as a frond.
New leaves expand by the unrolling of a tight spiral called a crozier or fiddlehead fern. This uncurling of the leaf is termed circinate vernation. Leaves are divided into a sporophyll. A trophophyll frond is a vegetative leaf analogous to the typical green leaves of seed plants that does not produce spores, instead only producing sugars by photosynthesis. A sporophyll frond is a fertile leaf that produces spores borne in sporangia that are clustered to form sori. In most ferns, fertile leaves are morphologically similar to the sterile ones, they photosynthesize in the same way. In some groups, the fertile leaves are much narrower than the sterile leaves, may have no green tissue at all; the anatomy of fern leaves can either be simple or divided. In tree ferns, the main stalk that connects the leaf to the stem has multiple leaflets; the leafy structures that grow from the stipe are known as pinnae and are again divided into smaller pinnules. Roots: The underground non-photosynthetic structures that take up water and nutrients from soil.
They are always fibrous and structurally are similar to the roots of seed plants. Like all other vascular plants, the diploid sporophyte is the dominant phase or generation in the life cycle; the gametophytes of ferns, are different from those of seed plants. They are free-living and resemble liverworts, whereas those of seed plants develop within the spore wall and are dependent on the parent sporophyte for their nutrition. A fern gametophyte consists of: Prothallus: A green, photosynthetic structure, one cell thick heart or kidney shaped, 3–10 mm long and 2–8 mm broad; the prothallus produces gametes by means of: Antheridia: Small spherical structures that produce flagellate sperm. Archegonia: A flask-shaped structure that produces a single egg at the bottom, reached by the sperm by swimming down the neck. Rhizoids: root-like structures that consist of single elongated cells, that absorb water and mineral salts over the whole structure. Rhizoids anchor the prothallus to the soil. Ferns first appear in the fossil record in the early Carboniferous period.
By the Triassic, the first evidence of ferns related to several modern families appeared. The great fern radiation occurred in the late Cretaceous, when many modern families of ferns first appeared. Ferns were traditionally classified in the class Filices, in a Division of the Plant Kingdom named Pteridophyta or Filicophyta. Pteridophyta is no longer recognised as a valid taxon; the ferns are referred to as Polypodiophyta or, when treated as a subdivision of Tracheophyta, although this name sometimes only refers to leptosporangiate ferns. Traditionally, all of the spore producing vascular plants were informally denominated the pteridophytes, rendering the term synonymous with ferns and fern allies; this can be confusing because members of the division Pteridophyta were denominated pteridophytes. Traditionally, three discrete groups have be
Cladistics
Cladistics is an approach to biological classification in which organisms are categorized in groups based on the most recent common ancestor. Hypothesized relationships are based on shared derived characteristics that can be traced to the most recent common ancestor and are not present in more distant groups and ancestors. A key feature of a clade is that all its descendants are part of the clade. All descendants stay in their overarching ancestral clade. For example, if within a strict cladistic framework the terms animals, bilateria/worms, fishes/vertebrata, or monkeys/anthropoidea were used, these terms would include humans. Many of these terms are used paraphyletically, outside of cladistics, e.g. as a'grade'. Radiation results in the generation of new subclades by bifurcation; the techniques and nomenclature of cladistics have been applied to other disciplines. Cladistics is now the most used method to classify organisms; the original methods used in cladistic analysis and the school of taxonomy derived from the work of the German entomologist Willi Hennig, who referred to it as phylogenetic systematics.
Cladistics in the original sense refers to a particular set of methods used in phylogenetic analysis, although it is now sometimes used to refer to the whole field. What is now called the cladistic method appeared as early as 1901 with a work by Peter Chalmers Mitchell for birds and subsequently by Robert John Tillyard in 1921, W. Zimmermann in 1943; the term "clade" was introduced in 1958 by Julian Huxley after having been coined by Lucien Cuénot in 1940, "cladogenesis" in 1958, "cladistic" by Cain and Harrison in 1960, "cladist" by Mayr in 1965, "cladistics" in 1966. Hennig referred to his own approach as "phylogenetic systematics". From the time of his original formulation until the end of the 1970s, cladistics competed as an analytical and philosophical approach to systematics with phenetics and so-called evolutionary taxonomy. Phenetics was championed at this time by the numerical taxonomists Peter Sneath and Robert Sokal, evolutionary taxonomy by Ernst Mayr. Conceived, if only in essence, by Willi Hennig in a book published in 1950, cladistics did not flourish until its translation into English in 1966.
Today, cladistics is the most popular method for constructing phylogenies from morphological data. In the 1990s, the development of effective polymerase chain reaction techniques allowed the application of cladistic methods to biochemical and molecular genetic traits of organisms, vastly expanding the amount of data available for phylogenetics. At the same time, cladistics became popular in evolutionary biology, because computers made it possible to process large quantities of data about organisms and their characteristics; the cladistic method interprets each character state transformation implied by the distribution of shared character states among taxa as a potential piece of evidence for grouping. The outcome of a cladistic analysis is a cladogram – a tree-shaped diagram, interpreted to represent the best hypothesis of phylogenetic relationships. Although traditionally such cladograms were generated on the basis of morphological characters and calculated by hand, genetic sequencing data and computational phylogenetics are now used in phylogenetic analyses, the parsimony criterion has been abandoned by many phylogeneticists in favor of more "sophisticated" but less parsimonious evolutionary models of character state transformation.
Cladists contend. Every cladogram is based on a particular dataset analyzed with a particular method. Datasets are tables consisting of molecular, ethological and/or other characters and a list of operational taxonomic units, which may be genes, populations, species, or larger taxa that are presumed to be monophyletic and therefore to form, all together, one large clade. Different datasets and different methods, not to mention violations of the mentioned assumptions result in different cladograms. Only scientific investigation can show, more to be correct; until for example, cladograms like the following have been accepted as accurate representations of the ancestral relations among turtles, lizards and birds: If this phylogenetic hypothesis is correct the last common ancestor of turtles and birds, at the branch near the ▼ lived earlier than the last common ancestor of lizards and birds, near the ♦. Most molecular evidence, produces cladograms more like this: If this is accurate the last common ancestor of turtles and birds lived than the last common ancestor of lizards and birds.
Since the cladograms provide competing accounts of real events, at most one of them is correct. The cladogram to the right represents the current universally accepted hypothesis that all primates, including strepsirrhines like the lemurs and lorises, had a common ancestor all of whose descendants were primates, so form a clade. Within the primates, all anthropoids are hypothesized to have had a common ancestor all of whose descendants were anthropoids, so they form the clade called Anthropoidea; the "prosimians", on the other hand, form a paraphyletic taxon. The name Prosimii is not used in phylogenetic nomenclature, whic
. Encyclopædia Britannica (11th ed.). 1911.
