Plant morphology

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Phytomorphology is the study of the physical form and external structure of plants. [1] This is usually considered distinct from plant anatomy, [1] which is the study of the internal structure of plants, especially at the microscopic level. [2] Plant morphology is useful in the visual identification of plants. Recent studies in molecular biology started to investigate the molecular processes involved in determining the conservation and diversification of plant morphologies. In these studies transcriptome conservation patterns were found to mark crucial ontogenetic transitions during the plant life cycle which may result in evolutionary constraints limiting diversification. [3]

Contents

Inflorescences emerging from protective coverings Angelica gigas.jpg
Inflorescences emerging from protective coverings

Scope

Asclepias syriaca showing complex morphology of the flowers. Asclepia syriaca3.jpg
Asclepias syriaca showing complex morphology of the flowers.
Looking up into the branch structure of a Pinus sylvestris tree Strom roka borovica velke borove 03.jpg
Looking up into the branch structure of a Pinus sylvestris tree
Animation of zooming into the leaf of a Sequoia sempervirens (Californian Redwood).

Plant morphology "represents a study of the development, form, and structure of plants, and, by implication, an attempt to interpret these on the basis of similarity of plan and origin". [4] There are four major areas of investigation in plant morphology, and each overlaps with another field of the biological sciences.

First of all, morphology is comparative , meaning that the morphologist examines structures in many different plants of the same or different species, then draws comparisons and formulates ideas about similarities. When structures in different species are believed to exist and develop as a result of common, inherited genetic pathways, those structures are termed homologous. For example, the leaves of pine, oak, and cabbage all look very different, but share certain basic structures and arrangement of parts. The homology of leaves is an easy conclusion to make. The plant morphologist goes further, and discovers that the spines of cactus also share the same basic structure and development as leaves in other plants, and therefore cactus spines are homologous to leaves as well. This aspect of plant morphology overlaps with the study of plant evolution and paleobotany.

Secondly, plant morphology observes both the vegetative (somatic) structures of plants, as well as the reproductive structures. The vegetative structures of vascular plants includes the study of the shoot system, composed of stems and leaves, as well as the root system. The reproductive structures are more varied, and are usually specific to a particular group of plants, such as flowers and seeds, fern sori, and moss capsules. The detailed study of reproductive structures in plants led to the discovery of the alternation of generations found in all plants and most algae. This area of plant morphology overlaps with the study of biodiversity and plant systematics.

Thirdly, plant morphology studies plant structure at a range of scales. At the smallest scales are ultrastructure , the general structural features of cells visible only with the aid of an electron microscope, and cytology , the study of cells using optical microscopy. At this scale, plant morphology overlaps with plant anatomy as a field of study. At the largest scale is the study of plant growth habit, the overall architecture of a plant. The pattern of branching in a tree will vary from species to species, as will the appearance of a plant as a tree, herb, or grass.

Fourthly, plant morphology examines the pattern of development, the process by which structures originate and mature as a plant grows. While animals produce all the body parts they will ever have from early in their life, plants constantly produce new tissues and structures throughout their life. A living plant always has embryonic tissues. The way in which new structures mature as they are produced may be affected by the point in the plant's life when they begin to develop, as well as by the environment to which the structures are exposed. A morphologist studies this process, the causes, and its result. This area of plant morphology overlaps with plant physiology and ecology.

A comparative science

A plant morphologist makes comparisons between structures in many different plants of the same or different species. Making such comparisons between similar structures in different plants tackles the question of why the structures are similar. It is quite likely that similar underlying causes of genetics, physiology, or response to the environment have led to this similarity in appearance. The result of scientific investigation into these causes can lead to one of two insights into the underlying biology:

  1. Homology - the structure is similar between the two species because of shared ancestry and common genetics.
  2. Convergence - the structure is similar between the two species because of independent adaptation to common environmental pressures.

Understanding which characteristics and structures belong to each type is an important part of understanding plant evolution. The evolutionary biologist relies on the plant morphologist to interpret structures, and in turn provides phylogenies of plant relationships that may lead to new morphological insights.

Homology

When structures in different species are believed to exist and develop as a result of common, inherited genetic pathways, those structures are termed homologous. For example, the leaves of pine, oak, and cabbage all look very different, but share certain basic structures and arrangement of parts. The homology of leaves is an easy conclusion to make. The plant morphologist goes further, and discovers that the spines of cactus also share the same basic structure and development as leaves in other plants, and therefore cactus spines are homologous to leaves as well.

Convergence

When structures in different species are believed to exist and develop as a result of common adaptive responses to environmental pressure, those structures are termed convergent. For example, the fronds of Bryopsis plumosa and stems of Asparagus setaceus both have the same feathery branching appearance, even though one is an alga and one is a flowering plant. The similarity in overall structure occurs independently as a result of convergence. The growth form of many cacti and species of Euphorbia is very similar, even though they belong to widely distant families. The similarity results from common solutions to the problem of surviving in a hot, dry environment.

Vegetative and reproductive characteristics

Plant.svg
A diagram representing a "typical" eudicot.

Plant morphology treats both the vegetative structures of plants, as well as the reproductive structures.

The vegetative (somatic) structures of vascular plants include two major organ systems: (1) a shoot system, composed of stems and leaves, and (2) a root system. These two systems are common to nearly all vascular plants, and provide a unifying theme for the study of plant morphology.

By contrast, the reproductive structures are varied, and are usually specific to a particular group of plants. Structures such as flowers and fruits are only found in the angiosperms; sori are only found in ferns; and seed cones are only found in conifers and other gymnosperms. Reproductive characters are therefore regarded as more useful for the classification of plants than vegetative characters.

Use in identification

Plant biologists use morphological characters of plants which can be compared, measured, counted and described to assess the differences or similarities in plant taxa and use these characters for plant identification, classification and descriptions.

When characters are used in descriptions or for identification they are called diagnostic or key characters which can be either qualitative and quantitative.

  1. Quantitative characters are morphological features that can be counted or measured for example a plant species has flower petals 10–12 mm wide.
  2. Qualitative characters are morphological features such as leaf shape, flower color or pubescence.

Both kinds of characters can be very useful for the identification of plants.

Alternation of generations

The detailed study of reproductive structures in plants led to the discovery of the alternation of generations, found in all plants and most algae, by the German botanist Wilhelm Hofmeister. This discovery is one of the most important made in all of plant morphology, since it provides a common basis for understanding the life cycle of all plants.

Pigmentation in plants

The primary function of pigments in plants is photosynthesis, which uses the green pigment chlorophyll along with several red and yellow pigments that help to capture as much light energy as possible the other pigments ic carotenoids'. Pigments are also an important factor in attracting insects to flowers to encourage pollination.

Plant pigments include a variety of different kinds of molecule, including porphyrins, carotenoids, anthocyanins and betalains. All biological pigments selectively absorb certain wavelengths of light while reflecting others. The light that is absorbed may be used by the plant to power chemical reactions, while the reflected wavelengths of light determine the color the pigment will appear to the eye.

Morphology in development

Plant development is the process by which structures originate and mature as a plant grows. It is a subject studies in plant anatomy and plant physiology as well as plant morphology.

The process of development in plants is fundamentally different from that seen in vertebrate animals. When an animal embryo begins to develop, it will very early produce all of the body parts that it will ever have in its life. When the animal is born (or hatches from its egg), it has all its body parts and from that point will only grow larger and more mature. By contrast, plants constantly produce new tissues and structures throughout their life from meristems [5] located at the tips of organs, or between mature tissues. Thus, a living plant always has embryonic tissues.

The properties of organisation seen in a plant are emergent properties which are more than the sum of the individual parts. "The assembly of these tissues and functions into an integrated multicellular organism yields not only the characteristics of the separate parts and processes but also quite a new set of characteristics which would not have been predictable on the basis of examination of the separate parts." [6] In other words, knowing everything about the molecules in a plant are not enough to predict characteristics of the cells; and knowing all the properties of the cells will not predict all the properties of a plant's structure.

Growth

A vascular plant begins from a single celled zygote, formed by fertilisation of an egg cell by a sperm cell. From that point, it begins to divide to form a plant embryo through the process of embryogenesis. As this happens, the resulting cells will organise so that one end becomes the first root, while the other end forms the tip of the shoot. In seed plants, the embryo will develop one or more "seed leaves" (cotyledons). By the end of embryogenesis, the young plant will have all the parts necessary to begin in its life.

Once the embryo germinates from its seed or parent plant, it begins to produce additional organs (leaves, stems, and roots) through the process of organogenesis. New roots grow from root meristems located at the tip of the root, and new stems and leaves grow from shoot meristems located at the tip of the shoot. [7] Branching occurs when small clumps of cells left behind by the meristem, and which have not yet undergone cellular differentiation to form a specialised tissue, begin to grow as the tip of a new root or shoot. Growth from any such meristem at the tip of a root or shoot is termed primary growth and results in the lengthening of that root or shoot. Secondary growth results in widening of a root or shoot from divisions of cells in a cambium. [8]

In addition to growth by cell division, a plant may grow through cell elongation. This occurs when individual cells or groups of cells grow longer. Not all plant cells will grow to the same length. When cells on one side of a stem grow longer and faster than cells on the other side, the stem will bend to the side of the slower growing cells as a result. This directional growth can occur via a plant's response to a particular stimulus, such as light (phototropism), gravity (gravitropism), water, (hydrotropism), and physical contact (thigmotropism).

Plant growth and development are mediated by specific plant hormones and plant growth regulators (PGRs) (Ross et al. 1983). [9] Endogenous hormone levels are influenced by plant age, cold hardiness, dormancy, and other metabolic conditions; photoperiod, drought, temperature, and other external environmental conditions; and exogenous sources of PGRs, e.g., externally applied and of rhizospheric origin.

Morphological variation

Plants exhibit natural variation in their form and structure. While all organisms vary from individual to individual, plants exhibit an additional type of variation. Within a single individual, parts are repeated which may differ in form and structure from other similar parts. This variation is most easily seen in the leaves of a plant, though other organs such as stems and flowers may show similar variation. There are three primary causes of this variation: positional effects, environmental effects, and juvenility.

Evolution of plant morphology

Transcription factors and transcriptional regulatory networks play key roles in plant morphogenesis and their evolution. During plant landing, many novel transcription factor families emerged and are preferentially wired into the networks of multicellular development, reproduction, and organ development, contributing to more complex morphogenesis of land plants. [10]

Positional effects

Variation in leaves from the giant ragweed illustrating positional effects. The lobed leaves come from the base of the plant, while the unlobed leaves come from the top of the plant. Leaf samples from the giant ragweed.jpg
Variation in leaves from the giant ragweed illustrating positional effects. The lobed leaves come from the base of the plant, while the unlobed leaves come from the top of the plant.

Although plants produce numerous copies of the same organ during their lives, not all copies of a particular organ will be identical. There is variation among the parts of a mature plant resulting from the relative position where the organ is produced. For example, along a new branch the leaves may vary in a consistent pattern along the branch. The form of leaves produced near the base of the branch will differ from leaves produced at the tip of the plant, and this difference is consistent from branch to branch on a given plant and in a given species. This difference persists after the leaves at both ends of the branch have matured, and is not the result of some leaves being younger than others.

Environmental effects

The way in which new structures mature as they are produced may be affected by the point in the plant's life when they begin to develop, as well as by the environment to which the structures are exposed. This can be seen in aquatic plants and emergent plants.

Temperature

Temperature has a multiplicity of effects on plants depending on a variety of factors, including the size and condition of the plant and the temperature and duration of exposure. The smaller and more succulent the plant, the greater the susceptibility to damage or death from temperatures that are too high or too low. Temperature affects the rate of biochemical and physiological processes, rates generally (within limits) increasing with temperature. However, the Van’t Hoff relationship for monomolecular reactions (which states that the velocity of a reaction is doubled or trebled by a temperature increase of 10 °C) does not strictly hold for biological processes, especially at low and high temperatures.

When water freezes in plants, the consequences for the plant depend very much on whether the freezing occurs intracellularly (within cells) or outside cells in intercellular (extracellular) spaces. [11] Intracellular freezing usually kills the cell regardless of the hardiness of the plant and its tissues. [12] Intracellular freezing seldom occurs in nature, but moderate rates of decrease in temperature, e.g., 1 °C to 6 °C/hour, cause intercellular ice to form, and this "extraorgan ice" [13] may or may not be lethal, depending on the hardiness of the tissue.

At freezing temperatures, water in the intercellular spaces of plant tissues freezes first, though the water may remain unfrozen until temperatures fall below 7 °C. [11] After the initial formation of ice intercellularly, the cells shrink as water is lost to the segregated ice. The cells undergo freeze-drying, the dehydration being the basic cause of freezing injury.

The rate of cooling has been shown to influence the frost resistance of tissues, [14] but the actual rate of freezing will depend not only on the cooling rate, but also on the degree of supercooling and the properties of the tissue. [15] Sakai (1979a) [14] demonstrated ice segregation in shoot primordia of Alaskan white and black spruces when cooled slowly to 30 °C to -40 °C. These freeze-dehydrated buds survived immersion in liquid nitrogen when slowly rewarmed. Floral primordia responded similarly. Extraorgan freezing in the primordia accounts for the ability of the hardiest of the boreal conifers to survive winters in regions when air temperatures often fall to -50 °C or lower. [13] The hardiness of the winter buds of such conifers is enhanced by the smallness of the buds, by the evolution of faster translocation of water, and an ability to tolerate intensive freeze dehydration. In boreal species of Picea and Pinus, the frost resistance of 1-year-old seedlings is on a par with mature plants, [16] given similar states of dormancy.

Juvenility

Juvenility in a seedling of European beech. There is a marked difference in shape between the first dark green "seed leaves" and the lighter second pair of leaves. Fagus sylvatica seed 001.jpg
Juvenility in a seedling of European beech. There is a marked difference in shape between the first dark green "seed leaves" and the lighter second pair of leaves.

The organs and tissues produced by a young plant, such as a seedling, are often different from those that are produced by the same plant when it is older. This phenomenon is known as juvenility or heteroblasty. For example, young trees will produce longer, leaner branches that grow upwards more than the branches they will produce as a fully grown tree. In addition, leaves produced during early growth tend to be larger, thinner, and more irregular than leaves on the adult plant. Specimens of juvenile plants may look so completely different from adult plants of the same species that egg-laying insects do not recognise the plant as food for their young. Differences are seen in rootability and flowering and can be seen in the same mature tree. Juvenile cuttings taken from the base of a tree will form roots much more readily than cuttings originating from the mid to upper crown. Flowering close to the base of a tree is absent or less profuse than flowering in the higher branches especially when a young tree first reaches flowering age. [17]

The transition from early to late growth forms is referred to as 'vegetative phase change', but there is some disagreement about terminology. [18]

Modern Innovations

Rolf Sattler has revised fundamental concepts of comparative morphology such as the concept of homology. He emphasised that homology should also include partial homology and quantitative homology. [19] [20] This leads to a continuum morphology that demonstrates a continuum between the morphological categories of root, shoot, stem (caulome), leaf (phyllome), and hair (trichome). How intermediates between the categories are best described has been discussed by Bruce K. Kirchoff et al. [21] A recent study conducted by Stalk Institute extracted coordinates corresponding to each plant's base and leaves in 3D space. When plants on the graph were placed according to their actual nutrient travel distances and total branch lengths, the plants fell almost perfectly on the Pareto curve. "This means the way plants grow their architectures also optimises a very common network design tradeoff. Based on the environment and the species, the plant is selecting different ways to make tradeoffs for those particular environmental conditions." [22]

Honoring Agnes Arber, author of the partial-shoot theory of the leaf, Rutishauser and Isler called the continuum approach Fuzzy Arberian Morphology (FAM). “Fuzzy” refers to fuzzy logic, “Arberian” to Agnes Arber. Rutishauser and Isler emphasised that this approach is not only supported by many morphological data but also by evidence from molecular genetics. [23] More recent evidence from molecular genetics provides further support for continuum morphology. James (2009) concluded that "it is now widely accepted that... radiality [characteristic of most stems] and dorsiventrality [characteristic of leaves] are but extremes of a continuous spectrum. In fact, it is simply the timing of the KNOX gene expression!." [24] Eckardt and Baum (2010) concluded that "it is now generally accepted that compound leaves express both leaf and shoot properties.” [25]

Process morphology describes and analyses the dynamic continuum of plant form. According to this approach, structures do not have process(es), they are process(es). [26] [27] [28] Thus, the structure/process dichotomy is overcome by "an enlargement of our concept of 'structure' so as to include and recognise that in the living organism it is not merely a question of spatial structure with an 'activity' as something over or against it, but that the concrete organism is a spatio-temporal structure and that this spatio-temporal structure is the activity itself". [29]

For Jeune, Barabé and Lacroix, classical morphology (that is, mainstream morphology, based on a qualitative homology concept implying mutually exclusive categories) and continuum morphology are sub-classes of the more encompassing process morphology (dynamic morphology). [30]

Classical morphology, continuum morphology, and process morphology are highly relevant to plant evolution, especially the field of plant evolutionary biology (plant evo-devo) that tries to integrate plant morphology and plant molecular genetics. [31] In a detailed case study on unusual morphologies, Rutishauser (2016) illustrated and discussed various topics of plant evo-devo such as the fuzziness (continuity) of morphological concepts, the lack of a one-to-one correspondence between structural categories and gene expression, the notion of morphospace, the adaptive value of bauplan features versus patio ludens, physiological adaptations, hopeful monsters and saltational evolution, the significance and limits of developmental robustness, etc. [32] Rutishauser (2020) discussed the past and future of plant evo-devo. [33] Our conception of the gynoecium and the search for a fossil ancestor of Angiosperms changes fundamentally from the perspective of evo-devo. [34]

Whether we like it or not, morphological research is influenced by philosophical assumptions such as either/or logic, fuzzy logic, structure/process dualism or its transcendence. And empirical findings may influence the philosophical assumptions. Thus there are interactions between philosophy and empirical findings. These interactions are the subject of what has been referred to as philosophy of plant morphology. [35]

One important and unique event in plant morphology of the 21st century was the publication of Kaplan's Principles of Plant Morphology by Donald R. Kaplan, edited by Chelsea D. Specht (2020). [36] It is a well illustrated volume of 1305 pages in a very large format that presents a wealth of morphological data. Unfortunately, all of these data are only interpreted in terms of classical morphology and the qualitative homology concept, disregarding modern conceptional innovations. [37] Including continuum and process morphology as well as molecular genetics would provide an enlarged scope. [38]

See also

Related Research Articles

<span class="mw-page-title-main">Botany</span> Science of plant life

Botany, also called plant science, 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 meaning "pasture", "herbs" "grass", or "fodder"; βοτάνη is in turn derived from βόσκειν, "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 study approximately 410,000 species of land plants of which some 391,000 species are vascular plants, and approximately 20,000 are bryophytes.

<span class="mw-page-title-main">Outline of biology</span> Outline of subdisciplines within biology

Biology – The natural science that studies life. Areas of focus include structure, function, growth, origin, evolution, distribution, and taxonomy.

Developmental biology is the study of the process by which animals and plants grow and develop. Developmental biology also encompasses the biology of regeneration, asexual reproduction, metamorphosis, and the growth and differentiation of stem cells in the adult organism.

<span class="mw-page-title-main">Root</span> Basal organ of a vascular plant

In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the surface of the soil, but roots can also be aerial or aerating, that is, growing up above the ground or especially above water.

<span class="mw-page-title-main">Meristem</span> Type of plant tissue involved in cell proliferation

The meristem is a type of tissue found in plants. It consists of undifferentiated cells capable of cell division. Cells in the meristem can develop into all the other tissues and organs that occur in plants. These cells continue to divide until a time when they get differentiated and then lose the ability to divide.

<span class="mw-page-title-main">Vegetative reproduction</span> Asexual method of reproduction in plants

Vegetative reproduction is a form of asexual reproduction occurring in plants in which a new plant grows from a fragment or cutting of the parent plant or specialized reproductive structures, which are sometimes called vegetative propagules.

Plant embryonic development, also plant embryogenesis is a process that occurs after the fertilization of an ovule to produce a fully developed plant embryo. This is a pertinent stage in the plant life cycle that is followed by dormancy and germination. The zygote produced after fertilization must undergo various cellular divisions and differentiations to become a mature embryo. An end stage embryo has five major components including the shoot apical meristem, hypocotyl, root meristem, root cap, and cotyledons. Unlike the embryonic development in animals, and specifically in humans, plant embryonic development results in an immature form of the plant, lacking most structures like leaves, stems, and reproductive structures. However, both plants and animals including humans, pass through a phylotypic stage that evolved independently and that causes a developmental constraint limiting morphological diversification.

<span class="mw-page-title-main">Alpine plant</span> Plants that grow at high elevation

Alpine plants are plants that grow in an alpine climate, which occurs at high elevation and above the tree line. There are many different plant species and taxa that grow as a plant community in these alpine tundra. These include perennial grasses, sedges, forbs, cushion plants, mosses, and lichens. Alpine plants are adapted to the harsh conditions of the alpine environment, which include low temperatures, dryness, ultraviolet radiation, wind, drought, poor nutritional soil, and a short growing season.

<span class="mw-page-title-main">Gynoecium</span> Female organs of a flower

Gynoecium is most commonly used as a collective term for the parts of a flower that produce ovules and ultimately develop into the fruit and seeds. The gynoecium is the innermost whorl of a flower; it consists of pistils and is typically surrounded by the pollen-producing reproductive organs, the stamens, collectively called the androecium. The gynoecium is often referred to as the "female" portion of the flower, although rather than directly producing female gametes, the gynoecium produces megaspores, each of which develops into a female gametophyte which then produces egg cells.

<span class="mw-page-title-main">Secondary growth</span> Type of growth in plants

In botany, secondary growth is the growth that results from cell division in the cambia or lateral meristems and that causes the stems and roots to thicken, while primary growth is growth that occurs as a result of cell division at the tips of stems and roots, causing them to elongate, and gives rise to primary tissue. Secondary growth occurs in most seed plants, but monocots usually lack secondary growth. If they do have secondary growth, it differs from the typical pattern of other seed plants.

<span class="mw-page-title-main">Primordium</span> Organ in the earliest recognizable stage of embryonic development

A primordium in embryology, is an organ or tissue in its earliest recognizable stage of development. Cells of the primordium are called primordial cells. A primordium is the simplest set of cells capable of triggering growth of the would-be organ and the initial foundation from which an organ is able to grow. In flowering plants, a floral primordium gives rise to a flower.

<span class="mw-page-title-main">Plant anatomy</span> Study of the internal structure of plants

Plant anatomy or phytotomy is the general term for the study of the internal structure of plants. Originally, it included plant morphology, the description of the physical form and external structure of plants, but since the mid-20th century, plant anatomy has been considered a separate field referring only to internal plant structure. Plant anatomy is now frequently investigated at the cellular level, and often involves the sectioning of tissues and microscopy.

Evolutionary developmental biology (evo-devo) is the study of developmental programs and patterns from an evolutionary perspective. It seeks to understand the various influences shaping the form and nature of life on the planet. Evo-devo arose as a separate branch of science rather recently. An early sign of this occurred in 1999.

Important structures in plant development are buds, shoots, roots, leaves, and flowers; plants produce these tissues and structures throughout their life from meristems located at the tips of organs, or between mature tissues. Thus, a living plant always has embryonic tissues. By contrast, an animal embryo will very early produce all of the body parts that it will ever have in its life. When the animal is born, it has all its body parts and from that point will only grow larger and more mature. However, both plants and animals pass through a phylotypic stage that evolved independently and that causes a developmental constraint limiting morphological diversification.

<span class="mw-page-title-main">Plant tissue culture</span> Growing cells under lab conditions

Plant tissue culture is a collection of techniques used to maintain or grow plant cells, tissues, or organs under sterile conditions on a nutrient culture medium of known composition. It is widely used to produce clones of a plant in a method known as micropropagation. Different techniques in plant tissue culture may offer certain advantages over traditional methods of propagation, including:

Rolf Sattler FLS FRSC is a Canadian plant morphologist, biologist, philosopher, and educator. He is considered one of the most significant contributors to the field of plant morphology and "one of the foremost plant morphologists in the world." His contributions are not only empirical but involved also a revision of the most fundamental concepts, theories, and philosophical assumptions. He published the award-winning Organogenesis of Flowers (1973) and nearly a hundred scientific papers, mainly on plant morphology. As well he has contributed to many national and international symposia and also organized and chaired symposia at international congresses, edited the proceedings of two of them and published them as books.

Primary growth in plants is growth that takes place from the tips of roots or shoots. It leads to lengthening of roots and stems and sets the stage for organ formation. It is distinguished from secondary growth that leads to widening. Plant growth takes place in well defined plant locations. Specifically, the cell division and differentiation needed for growth occurs in specialized structures called meristems. These consist of undifferentiated cells capable of cell division. Cells in the meristem can develop into all the other tissues and organs that occur in plants. These cells continue to divide until they differentiate and then lose the ability to divide. Thus, the meristems produce all the cells used for plant growth and function.

<span class="mw-page-title-main">Somatic embryogenesis</span> Method to derive a plant or embryo from a single somatic cell

Somatic embryogenesis is an artificial process in which a plant or embryo is derived from a single somatic cell. Somatic embryos are formed from plant cells that are not normally involved in the development of embryos, i.e. ordinary plant tissue. No endosperm or seed coat is formed around a somatic embryo.

CLE peptides are a group of peptides found in plants that are involved with cell signaling. Production is controlled by the CLE genes. Upon binding to a CLE peptide receptor in another cell, a chain reaction of events occurs, which can lead to various physiological and developmental processes. This signaling pathway is conserved in diverse land plants.

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