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Phytomorphology is the study of the physical form and external structure of
plant Plants are predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical energy that, through cellular respiration, can later be released to fuel ...

plant
s.Raven, P. H., R. F. Evert, & S. E. Eichhorn. ''Biology of Plants'', 7th ed., page 9. (New York: W. H. Freeman, 2005). . This is usually considered distinct from
plant anatomy Plant anatomy or phytotomy is the general term for the study of the internal structure A structure is an arrangement and organization of interrelated elements in a material object or system A system is a group of Interaction, interacting or ...
, which is the study of the internal
structure A structure is an arrangement and organization of interrelated elements in a material object or system A system is a group of Interaction, interacting or interrelated elements that act according to a set of rules to form a unified whole. A ...

structure
of plants, especially at the microscopic level. Plant morphology is useful in the visual identification of plants. Recent studies in
molecular biology Molecular biology is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, P ...
started to investigate the molecular processes involved in determining the conservation and diversification of plant morphologies. In these studies
transcriptome The transcriptome is the set of all RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, ...
conservation patterns were found to mark crucial
ontogenetic Ontogeny (also ontogenesis) is the origination and development of an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, ...
transitions during the
plant Plants are predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical energy that, through cellular respiration, can later be released to fuel ...

plant
life cycle which may result in evolutionary constraints limiting diversification.


Scope

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". There are four major areas of investigation in plant morphology, and each overlaps with another field of the
biological sciences Biology is the natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowl ...
. First of all, morphology is
comparative In general linguistics, the comparative is a syntactic construction that serves to express a comparison between two (or more) entities or groups of entities in quality or degree - see also comparison (grammar) for an overview of comparison, as well ...
, 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 pathways, those structures are termed homologous. For example, the
leaves A leaf (plural leaves) is the principal lateral appendage of the vascular plant plant stem, stem, usually borne above ground and specialized for photosynthesis. The leaves, stem, flower and fruit together form the shoot system. Leaves are ...

leaves
of
pine A pine is any conifer Conifers are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The divi ...

pine
,
oak An oak is a tree In botany, a tree is a perennial plant with an elongated Plant stem, stem, or trunk (botany), trunk, supporting branches and leaves in most species. In some usages, the definition of a tree may be narrower, including on ...

oak
, and
cabbage Cabbage, comprising several cultivars of ''Brassica oleracea ''Brassica oleracea'' is a plant species that includes many common foods as cultivars, including cabbage, broccoli, cauliflower, kale, Brussels sprouts, collard greens, Savoy cabba ...

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 A cactus (plural cacti, cactuses, or less commonly, cactus) is a member of the plant Plants are predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light en ...

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 Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; either through asexual reproduction or sexual reproduction, ...

evolution
and
paleobotany Paleobotany, which is also spelled as palaeobotany, is the branch of botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist ...
. Secondly, plant morphology observes both the vegetative (somatic) structures of plants, as well as the reproductive structures. The vegetative structures of
vascular plant Vascular plants (from Latin ''vasculum'': duct), also known as Tracheophyta (the tracheophytes , from Greek τραχεῖα ἀρτηρία ''trācheia artēria'' 'windpipe' + φυτά ''phutá'' 'plants'), form a large group of plants ( 300,000 ...
s includes the study of the shoot system, composed of and
leaves A leaf (plural leaves) is the principal lateral appendage of the vascular plant plant stem, stem, usually borne above ground and specialized for photosynthesis. The leaves, stem, flower and fruit together form the shoot system. Leaves are ...

leaves
, as well as the
root In vascular plant Vascular plants (from Latin ''vasculum'': duct), also known as Tracheophyta (the tracheophytes , from Greek τραχεῖα ἀρτηρία ''trācheia artēria'' 'windpipe' + φυτά ''phutá'' 'plants'), form a large grou ...

root
system. The reproductive structures are more varied, and are usually specific to a particular group of plants, such as
flower A flower, sometimes known as a bloom or blossom Image:Cerisier du Japon Prunus serrulata.jpg, Cherry blossoms in Paris in full bloom. In botany, blossoms are the flowers of stone fruit fruit tree, trees (genus ''Prunus'') and of some other plan ...

flower
s and
seed A seed is an embryonic ''Embryonic'' is the twelfth studio album by experimental rock band the Flaming Lips released on October 13, 2009, on Warner Bros. Records, Warner Bros. The band's first double album, it was released to generally positi ...

seed
s, fern sori, and
moss Mosses are small, non-vascular flower A flower, sometimes known as a bloom or blossom Cherry blossoms in Paris in full bloom. In botany, blossoms are the flowers of stone fruit fruit tree, trees (genus ''Prunus'') and of some other plant ...

moss
capsules. The detailed study of reproductive structures in plants led to the discovery of the
alternation of generations Alternation of generations (also known as metagenesis or heterogenesis) is the type of that occurs in those s and in the and the that have distinct haploid sexual and diploid asexual stages. In these groups, a with ''n'' s alternates with ...

alternation of generations
found in all plants and most
alga Algae (; singular alga ) is an informal term for a large and diverse group of photosynthesis, photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from un ...

alga
e. This area of plant morphology overlaps with the study of
biodiversity Biodiversity is the biological variety and Genetic variability, variability of life, life on Earth. Biodiversity is a measure of variation at the Genetics, genetic, species, and ecosystem level. Terrestrial biodiversity is usually greater near ...

biodiversity
and plant systematics. Thirdly, plant morphology studies plant structure at a range of scales. At the smallest scales are
ultrastructure The ultrastructure of a single bacterial cell ('' nm.">nanometer.html" ;"title="Bacillus subtilis''). The scale bar is 200 nanometer">nm. Ultrastructure (or ultra-structure) is the architecture of cells and biomaterials that is visible at higher ...
, the general structural features of cells visible only with the aid of an
electron microscope An electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination. As the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, electron microscopes have a high ...

electron microscope
, and
cytology Cell biology (also cellular biology or cytology) is a branch of biology studying the structure and function of the cell, also known as the basic unit of life Life is a characteristic that distinguishes physical entities that have bi ...
, the study of cells using
optical microscopy Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of optical instruments, instruments that use or Photodetector, detect it. Optics usually describes the ...
. At this scale, plant morphology overlaps with
plant anatomy Plant anatomy or phytotomy is the general term for the study of the internal structure A structure is an arrangement and organization of interrelated elements in a material object or system A system is a group of Interaction, interacting or ...
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 In botany, a tree is a perennial plant with an elongated Plant stem, stem, or trunk (botany), trunk, supporting branches and leaves in most species. In some usages, the definition of a tree may be narrower, including only wood plants with se ...

tree
will vary from species to species, as will the appearance of a plant as a
tree In botany, a tree is a perennial plant with an elongated Plant stem, stem, or trunk (botany), trunk, supporting branches and leaves in most species. In some usages, the definition of a tree may be narrower, including only wood plants with se ...

tree
,
herb In general use, herbs are a widely distributed and widespread group of plants, excluding vegetables Vegetables are parts of plants that are consumed by humans or other animals as food. The original meaning is still commonly used and is app ...

herb
, or
grass Poaceae () or Gramineae () is a large and nearly ubiquitous family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to maintain ...

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 Plant physiology is a subdiscipline of botany Botany, also called , 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. ...

plant physiology
and
ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms In biol ...
.


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: # Homology - the structure is similar between the two species because of shared ancestry and common genetics. #
Convergence Convergence may refer to: Arts and media Literature *Convergence (book series), ''Convergence'' (book series), edited by Ruth Nanda Anshen *Convergence (comics), "Convergence" (comics), two separate story lines published by DC Comics: **A four-par ...
- 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 Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; either through asexual reproduction or sexual reproduction, ...

evolution
. The evolutionary biologist relies on the plant morphologist to interpret structures, and in turn provides
phylogenies In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms, ...

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 '''' 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 A cactus (plural cacti, cactuses, or less commonly, cactus) is a member of the plant Plants are predominantly photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all living thi ...

cacti
and species of ''
Euphorbia ''Euphorbia'' is a very large and diverse genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV ...

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 morphology treats both the vegetative structures of plants, as well as the reproductive structures. The vegetative (somatic) structures of
vascular plant Vascular plants (from Latin ''vasculum'': duct), also known as Tracheophyta (the tracheophytes , from Greek τραχεῖα ἀρτηρία ''trācheia artēria'' 'windpipe' + φυτά ''phutá'' 'plants'), form a large group of plants ( 300,000 ...
s include two major organ systems: (1) a shoot system, composed of and
leaves A leaf (plural leaves) is the principal lateral appendage of the vascular plant plant stem, stem, usually borne above ground and specialized for photosynthesis. The leaves, stem, flower and fruit together form the shoot system. Leaves are ...

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
flower A flower, sometimes known as a bloom or blossom Image:Cerisier du Japon Prunus serrulata.jpg, Cherry blossoms in Paris in full bloom. In botany, blossoms are the flowers of stone fruit fruit tree, trees (genus ''Prunus'') and of some other plan ...

flower
s and
fruit In botany Botany, also called , 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 ...

fruit
s are only found in the
angiosperm Flowering plants include multiple members of the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ...

angiosperm
s; sori are only found in
fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plant Vascular plants (from Latin ''vasculum'': duct), also known as Tracheophyta (the tracheophytes , from Greek τραχεῖα ἀρτηρία ''trācheia art ...

fern
s; and seed cones are only found in
conifer Conifers are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single e ...
s 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. # Quantitative characters are morphological features that can be counted or measured for example a plant species has flower petals 10–12 mm wide. # 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 Alternation of generations (also known as metagenesis or heterogenesis) is the type of that occurs in those s and in the and the that have distinct haploid sexual and diploid asexual stages. In these groups, a with ''n'' s alternates with ...

alternation of generations
, found in all plants and most
alga Algae (; singular alga ) is an informal term for a large and diverse group of photosynthesis, photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from un ...

alga
e, by the German botanist
Wilhelm Hofmeister Wilhelm Friedrich Benedikt Hofmeister (18 May 1824 – 12 January 1877) was a German biologist Francesco Redi, the founder of biology, is recognized to be one of the greatest biologists of all time A biologist is a professional who has ...

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 Photosynthesis is a process used by plants and other organisms to convert Conversion or convert may refer to: Arts, entertainment, and media * Conversion (Doctor Who audio), "Conversion" (''Doctor Who'' audio), an episode of the audio drama ' ...

photosynthesis
, which uses the green pigment
chlorophyll Chlorophyll (also chlorophyl) is any of several related green pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally ...

chlorophyll
along with several red and yellow pigments that help to capture as much light energy as possible. Pigments are also an important factor in attracting
insect Insects (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in ...

insect
s to flowers to encourage
pollination Pollination is the transfer of pollen Pollen is a powdery substance consisting of pollen grains which are Sporophyte, microsporophytes of spermatophyta, seed plants, which produce male gametes (sperm cells). Pollen grains have a hard coat ...

pollination
. Plant pigments include a variety of different kinds of molecule, including
porphyrin Porphyrins ( ) are a group of heterocyclic 125px, Pyridine, a heterocyclic compound A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different chemical element, elements as members of its ring(s). ...

porphyrin
s,
carotenoid Carotenoids (), also called tetraterpenoids, are yellow, orange, and red organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), organ Chemistry * Organ ...
s,
anthocyanin Anthocyanins (also anthocyans; from Ancient Greek, Greek: (''anthos'') "flower" and / ''kyaneos/kyanous'' "dark blue") are solubility, water-soluble vacuole, vacuolar pigments that, depending on their pH, may appear red, purple, blue or black. F ...

anthocyanin
s and
betalain Betalains are a class of red and yellow tyrosine-derived pigments found in plants of the Caryophyllales, where they replace anthocyanin pigments. Betalains also occur in some higher order fungi. They are most often noticeable in the petals of fl ...
s. All biological pigments selectively absorb certain wavelengths of
light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that is visual perception, perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nan ...

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 Plant anatomy or phytotomy is the general term for the study of the internal structure A structure is an arrangement and organization of interrelated elements in a material object or system A system is a group of Interaction, interacting or ...
and
plant physiology Plant physiology is a subdiscipline of botany Botany, also called , 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. ...

plant physiology
as well as plant morphology. The process of development in plants is fundamentally different from that seen in
vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an indiv ...
animals. When an animal
embryo An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms ar ...

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
meristem The meristem is a type of tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ''Triphosa du ...
s located at the tips of organs, or between mature tissues. Thus, a living plant always has embryonic tissues. The properties of organization seen in a plant are
emergent properties In philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about reason, Metaphysics, existence, Epistemology, knowledge, Ethics, values, Philosophy of mind, mind, and Philosophy of language, ...

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." 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 Vascular plants (from Latin ''vasculum'': duct), also known as Tracheophyta (the tracheophytes , from Greek τραχεῖα ἀρτηρία ''trācheia artēria'' 'windpipe' + φυτά ''phutá'' 'plants'), form a large group of plants ( 300,000 ...
begins from a single celled
zygote A zygote (, ) is a eukaryotic Eukaryotes () are organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are ...

zygote
, formed by
fertilisation Fertilisation or fertilization (see American and British English spelling differences#-ise.2C -ize .28-isation.2C -ization.29, spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes ...

fertilisation
of an egg cell by a sperm cell. From that point, it begins to divide to form a plant
embryo An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms ar ...

embryo
through the process of embryogenesis. As this happens, the resulting cells will organize so that one end becomes the first root, while the other end forms the tip of the shoot. In
seed A seed is an embryonic ''Embryonic'' is the twelfth studio album by experimental rock band the Flaming Lips released on October 13, 2009, on Warner Bros. Records, Warner Bros. The band's first double album, it was released to generally positi ...

seed
plants, the embryo will develop one or more "seed leaves" (
cotyledon A cotyledon (; ; ; , gen. (), ) is a significant part of the embryo within the seed of a plant, and is defined as "the embryonic leaf in seed-bearing plants, one or more of which are the first to appear from a germination, germinating see ...
s). By the end of embryogenesis, the young plant will have all the parts necessary to begin in its life. Once the embryo 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
meristem The meristem is a type of tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ''Triphosa du ...
s located at the tip of the root, and new stems and leaves grow from shoot
meristem The meristem is a type of tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ''Triphosa du ...
s located at the tip of the shoot. Branching occurs when small clumps of cells left behind by the meristem, and which have not yet undergone
cellular differentiation Cellular differentiation is the process in which a cell changes from one cell type A cell type is a classification used to distinguish between morphologically or phenotypically distinct cell forms within a species In biology, a sp ...
to form a specialized 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 In botany Botany, also called , 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 Anc ...
results in widening of a root or shoot from divisions of cells in a
cambium A cambium (plural cambia or cambiums), in plants, is a tissue layer that provides partially undifferentiated cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic ...
. 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 File:Phototropism Diagram.svg, thumbnail, Auxin distribution controls phototropism. 1. Sunlight strikes the plant from directly above. Auxin (pink dots) encourages growth straight up. 2, 3, 4. Sunlight strikes the plant at an angle. Auxin is conc ...

phototropism
), gravity (
gravitropism Gravitropism (also known as geotropism) is a coordinated process of differential growth by a plant Plants are predominantly photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all ...
), water, ( hydrotropism), and physical contact (
thigmotropism Thigmotropism is a directional growth movement which occurs as a mechanosensory response to a touch stimulus. Thigmotropism is typically found in twining plants and tendrils, however plant biologists have also found thigmotropic responses in flowe ...
). Plant growth and development are mediated by specific
plant hormone Plant hormones (or phytohormones) are signal molecule In biology, cell signaling (cell signalling in British English), or cell-cell communication, governs the basic activities of cell (biology), cells and coordinates multiple-cell actions. A si ...
s and plant growth regulators (PGRs) (Ross et al. 1983).Ross, S.D.; Pharis, R.P.; Binder, W.D. 1983. Growth regulators and conifers: their physiology and potential uses in forestry. p. 35–78 ''in'' Nickell, L.G. (Ed.), Plant growth regulating chemicals. Vol. 2, CRC Press, Boca Raton FL. 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.


Positional effects

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 plants life when they begin to develop, as well as by the environment to which the structures are exposed. This can be seen in
aquatic plant Aquatic plants are plant Plants are predominantly photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; howeve ...
s and
emergent plant Aquatic plants are plants that have adapted to living in aquatic environments (seawater, saltwater or freshwater). They are also referred to as hydrophytes or macrophytes to distinguish them from algae and other microphytes. A macrophyte is a pla ...
s.


=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.Glerum, C. 1985. Frost hardiness of coniferous seedlings: principles and applications. p. 107–123 ''in ''Duryea, M.L. (Ed.). Proceedings: Evaluating seedling quality: principles, procedures, and predictive abilities of major tests. Workshop, October 1984, Oregon State Univ., For. Res. Lab., Corvallis OR. Intracellular freezing usually kills the cell regardless of the hardiness of the plant and its tissues.Lyons, J.M.; Raison, J.K.; Steponkus, P.L. 1979. The plant membrane in response to low temperature: an overview. p. 1–24 ''in'' Lyons, J.M.; Graham, D.; Raison, J.K. (Eds.). Low Temperature Stress in Crop Plants. Academic Press, New York NY. 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"Sakai, A.; Larcher, W. (Eds.) 1987. Frost Survival of Plants. Springer-Verlag. 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. 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,Sakai, A. 1979a. Freezing avoidance mechanism of primordial shoots of conifer buds. Plant Cell Physiol. 20:1381–1390. 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.Levitt, J. 1980. Responses of Plants to Environmental Stresses. Volume 1. Chilling, Freezing, and High Temperature Stresses, 2nd ed. Academic Press, New York NY. 497 p. Sakai (1979a) 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 Students preparing homemade dewar of liquid nitrogen.">Cryogenic_storage_dewar.html" ;"title="ice cream with a Cryogenic storage dewar">dewar of liquid nitrogen. Liquid nitrogen—LN2—is nitrogen in a liquid state at low temperature. Liquid ...

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. The hardiness of the winter buds of such
conifers Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All exta ...

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,Sakai, A.; Okada, S. 1971. Freezing resistance of conifers. Silvae Genet. 20(3):91–97. given similar states of dormancy.


Juvenility

The organs and tissues produced by a young plant, such as a
seedling A seedling is a young sporophyte '' Tortula muralis''. In mosses, the gametophyte is the dominant generation, while the sporophytes consist of sporangium-bearing stalks growing from the tips of the gametophytes A sporophyte () is the dip ...

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 recognize 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. The transition from early to late growth forms is referred to as '
vegetative phase changeVegetative phase change is the juvenile (organism), juvenile-to-adult transition in plants. This transition is distinct from the Flower#Flowering transition, reproductive transition and is most prolonged and pronounced in Woody plant, woody species. ...
', but there is some disagreement about terminology.


Modern Innovations

Rolf Sattler Rolf Sattler FLSFLS may refer to: Places * Flinders Island Airport, in Tasmania, Australia * Fordham Law School in New York City * Free Library of Springfield Township in Wyndmoor, Pennsylvania, United States * Frontline States, a defunct South ...
has revised fundamental concepts of comparative morphology such as the concept of homology. He emphasized that homology should also include partial homology and quantitative homology. 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. 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 optimizes 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." 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 In fuzzy mathematics, fuzzy logic is a form of many-valued logic in which the truth value Truth is the property of being in accord with fact or reality.Merriam-Webster's Online Dictionarytruth 2005 In everyday language, truth is typically ...

fuzzy logic
, “Arberian” to
Agnes Arber Agnes Robertson Arber FRS (23 February 1879 – 22 March 1960) was a British plant morphologist and anatomist, historian of botany and philosopher of biology. She was born in London but lived most of her life in Cambridge Cambridge ( ) i ...
. Rutishauser and Isler emphasized that this approach is not only supported by many morphological data but also by evidence from molecular genetics. More recent evidence from molecular genetics provides further support for continuum morphology. James (2009) concluded that "it is now widely accepted that... radiality haracteristic of most stemsand dorsiventrality haracteristic of leavesare but extremes of a continuous spectrum. In fact, it is simply the timing of the KNOX gene expression!." Eckardt and Baum (2010) concluded that "it is now generally accepted that compound leaves express both leaf and shoot properties.” Process morphology describes and analyzes the dynamic continuum of plant form. According to this approach, structures do not ''have'' process(es), they ''are'' process(es). Thus, the structure/process dichotomy is overcome by "an enlargement of our concept of 'structure' so as to include and recognize 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". 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). 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. 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. Rutishauser (2020) discussed the past and future of plant evo-devo. 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.(for an expanded version of this article see

')


See also

*
Glossary of plant morphology This page provides a glossary of plant morphology. Botanists and other biologists who study plant morphology Phytomorphology is the study of the physical form and external structure of plant Plants are predominantly photosynthetic ...
*
Plant anatomy Plant anatomy or phytotomy is the general term for the study of the internal structure A structure is an arrangement and organization of interrelated elements in a material object or system A system is a group of Interaction, interacting or ...
*
Plant identification In biology, determination is the process of matching a specimen of an organism to a known taxon In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, ch ...
*
Plant physiology Plant physiology is a subdiscipline of botany Botany, also called , 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. ...

Plant physiology
* Plant evolutionary developmental biology *
Taxonomy Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a specific classification scheme. Originally used only about biological ...


References


External links


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