Timeline of plant evolution
Encyclopedia
This article attempts to place key plant innovations in a geological context. It concerns itself only with novel adaptations and events that had a major ecological significance, not those that are of solely anthropological interest. The timeline displays a graphical representation of the adaptations; the text attempts to explain the nature and robustness of the evidence.
Plant evolution is an aspect of the study of biological evolution, involving predominantly evolution of plants suited to live on land, greening of various land masses by the filling of their niches
with land plants, and diversification of groups of land plants.
kingdom Plantae. However, other photosynthetic organisms, including protists, green algae
, and cyanobacteria have evolutionary significance to modern plants. While this article is directly about the evolutionary history of the Plant kingdom, these other organisms provide clues to the evolution of all photosynthetic
organisms. All of these organisms - plants, green algae, and the protists - are primary photosynthetic eukaryotic organisms.
Scientists start the search for fossil evidence of plants with indirect evidence for their presence, the evidence of photosynthesis in the geological record. The evidence for photosynthesis in the rock record is varied, but primary evidence comes from around 3000 Ma, in rock records and fossil evidence of cyanobacteria, photosynthesizing prokaryotic organisms. Cyanobacteria use water as a reducing agent
, thereby producing atmospheric oxygen as a byproduct, and profoundly changing the early reducing atmosphere of the earth to one in which modern aerobic organisms eventually evolved. This oxygen liberated by cyanobacteria then oxidized
dissolved iron
in the oceans, the iron precipitated out of the sea water, and fell to the ocean floor to form sedimentary layers of oxidized iron called Banded Iron Formation
s (BIFs). These BIFs are part of the geological record of evidence for the evolutionary history of plants by identifying when photosynthesis originated. This also provides deep time constraints upon when enough oxygen could have been available in the atmosphere to produce the ultraviolet blocking stratospheric
ozone layer. The oxygen concentration in the ancient atmosphere subsequently rose, acting as a poison for anaerobic
organisms, and resulting in a highly oxidizing atmosphere, and opening up niches on land for occupation by aerobic organisms.
Evidence for the cyanobacteria also comes from the presence of stromatolite
s in the fossil record deep into the Precambrian
. Stromatolites are layered structures thought to have been formed by the trapping, binding, and cementation of sedimentary grains by microorganisms, such as cyanobacteria. The direct evidence for cyanobacteria is less certain than the evidence for their presence as primary producers of atmospheric oxygen. Modern day stromatoloid structures containing cyanobacteria can be found on the west coast of Australia.
Chloroplasts in eukaryotic plants evolved from an endosymbiotic
relationship between cyanobacteria and other prokaryotic organisms producing the lineage that eventually led to photosynthesizing eukaryotic organisms in marine and freshwater environments. These earliest photosynthesizing single-celled autotrophs later led to organisms such as Charophyta
, a group of freshwater green algae.
Cambrian
Early plants were small, unicellular or filamentous, composed mostly of soft body tissues, with simple branching. The identification of plant tissues in Cambrian strata is an uncertain area in the evolutionary history of plants because of the small and soft-bodied nature of these plants. It is also difficult in a fossil of this age to distinguish among various similar appearing groups with simple branching patterns, and not all of these groups are plants. One exception to the uncertainty of fossils from this age is the calcareous green algae, Dasycladales
found in the fossil record since the middle Cambrian. This algae does not belong to the lineage that is ancestral to the land plants. Other major groups of green algae had been established by this time. Generally it is accepted that there were no land plants with vascular tissues at this time although some biologist
s believe that the molecular clock points to an earlier Cambrian
or perhaps Precambrian
origin because the molecular clock states that land plants appeared around 480–440 Ma and fungi appeared on land around 1 Ga, however there is debate over whether the fossil evidence supports this interpretation of the molecular clock.
Ordovician
The evidence for plant evolutionary history changes dramatically in the Ordovician with the first extensive appearance of spores in the fossil record (Cambrian spores have been found, also). The first terrestrial plant
s appeared in the form of tiny plants resembling liverwort
s when, around the Middle Ordovician, evidence for the beginning of the terrestrialization of the land is found. These early plants did not have conducting tissues, severely limiting their size. They were, in effect, tied to wet terrestrial environments by their inability to conduct water, like extant liverworts, hornworts, and mosses, although they reproduced with spores, important dispersal units that have hard protective outer coatings, allowing for their preservation in the fossil record, in addition to protecting the future offspring against the desiccating environment of life on land. With spores, plants on land could have sent out large numbers of spores that could grow into an adult plant when sufficient environmental moisture was present.
Silurian
The first fossil records of vascular plant
s, that is, land plants with vascular tissue
s, appeared in the Silurian period. The earliest known representatives of this group are Cooksonia
(mostly from the northern hemisphere) and Baragwanathia
(from Australia). A primitive Silurian land plant with xylem
and phloem
but no differentiation in root, stem or leaf, was much-branched Psilophyton
, reproducing by spore
s and breathing through stomata on every surface, and probably photosynthesizing
in every tissue exposed to light. Rhyniophyta
and primitive lycopod
s were other land plants that first appear during this period.
Devonian
By the Devonian Period, life was well underway in its colonization of the land. The bacterial and algal mats were joined early in the period by primitive plant
s that created the first recognizable soil
s and harbored some arthropods like mite
s, scorpion
s and myriapods. Early Devonian plants did not have roots or leaves like the plants most common today, and many had no vascular tissue at all. They probably spread largely by vegetative growth, and did not grow much more than a few centimeters tall.
By the Late Devonian, forests of small, primitive plants existed: lycophytes, sphenophytes, fern
s, and progymnosperms had evolved
. Most of these plants have true roots and leaves, and many were quite tall. The tree-like ancestral fern Archaeopteris
and the giant cladoxylopsid
trees grew as a large tree with true wood
. These are the oldest known trees of the world's first forests. Prototaxites
was the fruiting body of an enormous fungus that stood more than 8 meter tall. By the end of the Devonian, the first seed-forming plants had appeared. This rapid appearance of so many plant groups and growth forms has been called the "Devonian Explosion". The primitive arthropods co-evolved with this diversified terrestrial vegetation structure. The evolving co-dependence of insects and seed-plants that characterizes a recognizably modern world had its genesis in the late Devonian. The development of soils and plant root systems probably led to changes in the speed and pattern of erosion
and sediment deposition.
The 'greening' of the continents acted as a carbon dioxide
sink
, and atmospheric
levels of this greenhouse gas
may have dropped. This may have cooled the climate and led to a massive extinction event
. see Late Devonian extinction
.
Also in the Devonian, both vertebrate
s and arthropods were solidly established on the land.
Carboniferous
Early Carboniferous land plants were very similar to those of the preceding Latest Devonian, but new groups also appeared at this time.
The main Early Carboniferous plants were the Equisetales
(Horse-tails), Sphenophyllales
(scrambling plants), Lycopodiales (Club mosses), Lepidodendrales
(scale trees), Filicales (Ferns), Medullosales
(previously included in the "seed ferns
", an artificial assemblage of a number of early gymnosperm
groups) and the Cordaitales
. These continued to dominate throughout the period, but during late Carboniferous
, several other groups, Cycadophyta (cycads), the Callistophytales
(another group of "seed ferns"), and the Voltziales
(related to and sometimes included under the conifers), appeared.
The Carboniferous lycophytes of the order Lepidodendrales, which are cousins (but not ancestors) of the tiny club-moss of today, were huge trees with trunks 30 meters high and up to 1.5 meters in diameter. These included Lepidodendron
(with its fruit cone called Lepidostrobus), Halonia, Lepidophloios and Sigillaria
. The roots of several of these forms are known as Stigmaria
.
The fronds of some Carboniferous ferns are almost identical with those of living species. Probably many species were epiphytic. Fossil ferns and "seed ferns" include Pecopteris
, Cyclopteris, Neuropteris
, Alethopteris
, and Sphenopteris; Megaphyton and Caulopteris were tree ferns.
The Equisetales included the common giant form Calamites
, with a trunk diameter of 30 to 60 cm and a height of up to 20 meters. Sphenophyllum
was a slender climbing plant with whorls of leaves, which was probably related both to the calamites and the lycopods.
Cordaites
, a tall plant (6 to over 30 meters) with strap-like leaves, was related to the cycads and conifers; the catkin
-like inflorescence, which bore yew-like berries, is called Cardiocarpus. These plants were thought to live in swamps and mangroves. True coniferous trees (Walchia
, of the order Voltziales) appear later in the Carboniferous, and preferred higher drier ground.
Permian
The Permian began with the Carboniferous flora still flourishing. About the middle of the Permian there was a major transition in vegetation. The swamp-loving lycopod trees of the Carboniferous, such as Lepidodendron
and Sigillaria
, were replaced by the more advanced conifers, which were better adapted to the changing climatic conditions. Lycopods and swamp forests still dominated the South China
continent because it was an isolated continent and it sat near or at the equator. Oxygen levels were probably high there. The Permian saw the radiation of many important conifer groups, including the ancestors of many present-day families. The ginkgo
s and cycads also appeared during this period. Rich forests were present in many areas, with a diverse mix of plant groups. The gigantopterid
s thrived during this time; some of these may have been part of the ancestral flowering plant
lineage, though flowers evolved only considerably later.
Triassic
On land, the holdover plants included the lycophytes, the dominant cycad
s, ginkgophyta (represented in modern times by Ginkgo biloba
) and glossopterid
s. The spermatophyte
s, or seed plants came to dominate the terrestrial flora: in the northern hemisphere, conifers flourished. Dicroidium
(a seed fern) was the dominant southern hemisphere tree during the Early Triassic period.
Jurassic
The arid, continental conditions characteristic of the Triassic steadily eased during the Jurassic period, especially at higher latitudes; the warm, humid climate allowed lush jungles to cover much of the landscape. Conifers dominated the flora, as during the Triassic; they were the most diverse group and constituted the majority of large trees. Extant conifer families that flourished during the Jurassic included the Araucariaceae
, Cephalotaxaceae
, Pinaceae
, Podocarpaceae
, Taxaceae
and Taxodiaceae
. The extinct Mesozoic conifer family Cheirolepidiaceae
dominated low latitude vegetation, as did the shrubby Bennettitales
. Cycad
s were also common, as were ginkgo
s and tree ferns in the forest. Smaller fern
s were probably the dominant undergrowth. Caytoniaceous seed ferns were another group of important plants during this time and are thought to have been shrub to small-tree sized. Ginkgo-like plants were particularly common in the mid- to high northern latitudes. In the Southern Hemisphere, podocarps were especially successful, while Ginkgos and Czekanowskiales were rare.
Cretaceous
Flowering plants, also known as angiosperms, spread during this period, although they did not become predominant until near the end of the period (Campanian age
). Their evolution was aided by the appearance of bee
s; in fact angiosperms and insects are a good example of coevolution. The first representatives of many modern trees, including fig
s, planes
and magnolia
s, appeared in the Cretaceous. At the same time, some earlier Mesozoic gymnosperm
s, like Conifers continued to thrive, although other taxa like Bennettitales
died out before the end of the period.
About ten thousand years ago, humans in the Fertile Crescent
of the Middle East develop agriculture. Plant domestication begins with cultivation of Neolithic
founder crops. This process of food production, coupled later with the domestication of animals caused a massive increase in human population that has continued to the present. In Jericho (modern Israel), there is a settlement with about 19,000 people. At the same time, Sahara is green with rivers, lakes, cattles, crocodiles and monsoons.
At 8 ka, Common (Bread) wheat (Triticum aestivum) originates in southwest Asia due to hybridisation of emmer wheat with a goat-grass, Aegilops tauschii.
At 6.5 ka, two rice species are domesticated: Asian rice, Oryza sativa
, and African rice Oryza glaberrima.
Plant evolution is an aspect of the study of biological evolution, involving predominantly evolution of plants suited to live on land, greening of various land masses by the filling of their niches
Ecological niche
In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food...
with land plants, and diversification of groups of land plants.
Earliest classifiable plants
In the strictly modern sense, the name plant refers to the biological classificationBiological classification
Biological classification, or scientific classification in biology, is a method to group and categorize organisms by biological type, such as genus or species. Biological classification is part of scientific taxonomy....
kingdom Plantae. However, other photosynthetic organisms, including protists, green algae
Green algae
The green algae are the large group of algae from which the embryophytes emerged. As such, they form a paraphyletic group, although the group including both green algae and embryophytes is monophyletic...
, and cyanobacteria have evolutionary significance to modern plants. While this article is directly about the evolutionary history of the Plant kingdom, these other organisms provide clues to the evolution of all photosynthetic
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
organisms. All of these organisms - plants, green algae, and the protists - are primary photosynthetic eukaryotic organisms.
Scientists start the search for fossil evidence of plants with indirect evidence for their presence, the evidence of photosynthesis in the geological record. The evidence for photosynthesis in the rock record is varied, but primary evidence comes from around 3000 Ma, in rock records and fossil evidence of cyanobacteria, photosynthesizing prokaryotic organisms. Cyanobacteria use water as a reducing agent
Reducing agent
A reducing agent is the element or compound in a reduction-oxidation reaction that donates an electron to another species; however, since the reducer loses an electron we say it is "oxidized"...
, thereby producing atmospheric oxygen as a byproduct, and profoundly changing the early reducing atmosphere of the earth to one in which modern aerobic organisms eventually evolved. This oxygen liberated by cyanobacteria then oxidized
Oxidizing agent
An oxidizing agent can be defined as a substance that removes electrons from another reactant in a redox chemical reaction...
dissolved iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
in the oceans, the iron precipitated out of the sea water, and fell to the ocean floor to form sedimentary layers of oxidized iron called Banded Iron Formation
Banded iron formation
Banded iron formations are distinctive units of sedimentary rock that are almost always of Precambrian age. A typical BIF consists of repeated, thin layers of iron oxides, either magnetite or hematite , alternating with bands of iron-poor shale and chert...
s (BIFs). These BIFs are part of the geological record of evidence for the evolutionary history of plants by identifying when photosynthesis originated. This also provides deep time constraints upon when enough oxygen could have been available in the atmosphere to produce the ultraviolet blocking stratospheric
Stratosphere
The stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler...
ozone layer. The oxygen concentration in the ancient atmosphere subsequently rose, acting as a poison for anaerobic
Anaerobic organism
An anaerobic organism or anaerobe is any organism that does not require oxygen for growth. It could possibly react negatively and may even die if oxygen is present...
organisms, and resulting in a highly oxidizing atmosphere, and opening up niches on land for occupation by aerobic organisms.
Evidence for the cyanobacteria also comes from the presence of stromatolite
Stromatolite
Stromatolites or stromatoliths are layered accretionary structures formed in shallow water by the trapping, binding and cementation of sedimentary grains by biofilms of microorganisms, especially cyanobacteria ....
s in the fossil record deep into the Precambrian
Precambrian
The Precambrian is the name which describes the large span of time in Earth's history before the current Phanerozoic Eon, and is a Supereon divided into several eons of the geologic time scale...
. Stromatolites are layered structures thought to have been formed by the trapping, binding, and cementation of sedimentary grains by microorganisms, such as cyanobacteria. The direct evidence for cyanobacteria is less certain than the evidence for their presence as primary producers of atmospheric oxygen. Modern day stromatoloid structures containing cyanobacteria can be found on the west coast of Australia.
Chloroplasts in eukaryotic plants evolved from an endosymbiotic
Endosymbiotic theory
The endosymbiotic theory concerns the mitochondria, plastids , and possibly other organelles of eukaryotic cells. According to this theory, certain organelles originated as free-living bacteria that were taken inside another cell as endosymbionts...
relationship between cyanobacteria and other prokaryotic organisms producing the lineage that eventually led to photosynthesizing eukaryotic organisms in marine and freshwater environments. These earliest photosynthesizing single-celled autotrophs later led to organisms such as Charophyta
Charophyta
The Charophyta are a division of green algae, including the closest relatives of the embryophyte plants. In some groups, such as conjugating green algae, flagellate cells do not occur. The latter group does engage in sexual reproduction, and motility does not involve flagella, since they are...
, a group of freshwater green algae.
CambrianCambrianThe Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...
flora
Early plants were small, unicellular or filamentous, composed mostly of soft body tissues, with simple branching. The identification of plant tissues in Cambrian strata is an uncertain area in the evolutionary history of plants because of the small and soft-bodied nature of these plants. It is also difficult in a fossil of this age to distinguish among various similar appearing groups with simple branching patterns, and not all of these groups are plants. One exception to the uncertainty of fossils from this age is the calcareous green algae, DasycladalesDasycladales
In taxonomy, the Dasycladales is an order of large unicellular green algae in the class Ulvophyceae. It contains two families, the Dasycladaceae and the Polyphysaceae....
found in the fossil record since the middle Cambrian. This algae does not belong to the lineage that is ancestral to the land plants. Other major groups of green algae had been established by this time. Generally it is accepted that there were no land plants with vascular tissues at this time although some biologist
Biologist
A biologist is a scientist devoted to and producing results in biology through the study of life. Typically biologists study organisms and their relationship to their environment. Biologists involved in basic research attempt to discover underlying mechanisms that govern how organisms work...
s believe that the molecular clock points to an earlier Cambrian
Cambrian
The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...
or perhaps Precambrian
Precambrian
The Precambrian is the name which describes the large span of time in Earth's history before the current Phanerozoic Eon, and is a Supereon divided into several eons of the geologic time scale...
origin because the molecular clock states that land plants appeared around 480–440 Ma and fungi appeared on land around 1 Ga, however there is debate over whether the fossil evidence supports this interpretation of the molecular clock.
OrdovicianOrdovicianThe Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
flora
The evidence for plant evolutionary history changes dramatically in the Ordovician with the first extensive appearance of spores in the fossil record (Cambrian spores have been found, also). The first terrestrial plantPlant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
s appeared in the form of tiny plants resembling liverwort
Marchantiophyta
The Marchantiophyta are a division of bryophyte plants commonly referred to as hepatics or liverworts. Like other bryophytes, they have a gametophyte-dominant life cycle, in which cells of the plant carry only a single set of genetic information....
s when, around the Middle Ordovician, evidence for the beginning of the terrestrialization of the land is found. These early plants did not have conducting tissues, severely limiting their size. They were, in effect, tied to wet terrestrial environments by their inability to conduct water, like extant liverworts, hornworts, and mosses, although they reproduced with spores, important dispersal units that have hard protective outer coatings, allowing for their preservation in the fossil record, in addition to protecting the future offspring against the desiccating environment of life on land. With spores, plants on land could have sent out large numbers of spores that could grow into an adult plant when sufficient environmental moisture was present.
SilurianSilurianThe Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...
flora
Vascular plant
Vascular plants are those plants that have lignified tissues for conducting water, minerals, and photosynthetic products through the plant. Vascular plants include the clubmosses, Equisetum, ferns, gymnosperms and angiosperms...
s, that is, land plants with vascular tissue
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 xylem and phloem. These two tissues transport fluid and nutrients internally. There are also two meristems associated with vascular tissue:...
s, appeared in the Silurian period. The earliest known representatives of this group are Cooksonia
Cooksonia
Cooksonia is an extinct grouping of primitive land plants. The earliest Cooksonia date from the middle of the Silurian ; the group continues to be an important component of the flora until the Early Devonian, a total time span of...
(mostly from the northern hemisphere) and Baragwanathia
Baragwanathia
Baragwanathia is a genus of extinct plants of the division Lycopodiophyta of Late Silurian to Early Devonian age , fossils of which have been found in Australia, Canada and China.-Description:...
(from Australia). A primitive Silurian land plant with xylem
Xylem
Xylem is one of the two types of transport tissue in vascular plants. . The word xylem is derived from the Classical Greek word ξυλον , meaning "wood"; the best-known xylem tissue is wood, though it is found throughout the plant...
and phloem
Phloem
In vascular plants, phloem is the living tissue that carries organic nutrients , in particular, glucose, a sugar, to all parts of the plant where needed. In trees, the phloem is the innermost layer of the bark, hence the name, derived from the Greek word "bark"...
but no differentiation in root, stem or leaf, was much-branched Psilophyton
Psilophyton
Psilophyton is a genus of extinct vascular plants. Described in 1859, it was one of the first fossil plants to be found which was of Devonian age . Specimens have been found in northern Maine, USA; Gaspé Bay, Quebec and New Brunswick, Canada; the Czech Republic; and Yunnan, China...
, reproducing by spore
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
s and breathing through stomata on every surface, and probably photosynthesizing
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
in every tissue exposed to light. Rhyniophyta
Rhyniophyta
Rhyniopsida is a class of extinct early vascular plants, with one family, Rhyniaceae, found in the Early Devonian . They are polysporangiophytes, since their sporophytes consisted of branched stems bearing sporangia . They lacked leaves or true roots but did have simple vascular tissue...
and primitive lycopod
Lycopodiophyta
The Division Lycopodiophyta is a tracheophyte subdivision of the Kingdom Plantae. It is the oldest extant vascular plant division at around 410 million years old, and includes some of the most "primitive" extant species...
s were other land plants that first appear during this period.
DevonianDevonianThe Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
flora
By the Devonian Period, life was well underway in its colonization of the land. The bacterial and algal mats were joined early in the period by primitive plantPlant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
s that created the first recognizable soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
s and harbored some arthropods like mite
Mite
Mites, along with ticks, are small arthropods belonging to the subclass Acari and the class Arachnida. The scientific discipline devoted to the study of ticks and mites is called acarology.-Diversity and systematics:...
s, scorpion
Scorpion
Scorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. They have eight legs and are easily recognized by the pair of grasping claws and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger...
s and myriapods. Early Devonian plants did not have roots or leaves like the plants most common today, and many had no vascular tissue at all. They probably spread largely by vegetative growth, and did not grow much more than a few centimeters tall.
By the Late Devonian, forests of small, primitive plants existed: lycophytes, sphenophytes, fern
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
s, and progymnosperms had evolved
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
. Most of these plants have true roots and leaves, and many were quite tall. The tree-like ancestral fern Archaeopteris
Archaeopteris
Archaeopteris is an extinct genus of tree-like plants with fern-like leaves. A useful index fossil, this tree is found in strata dating from the Upper Devonian to Lower Carboniferous , and has a global distribution....
and the giant cladoxylopsid
Cladoxylopsid
The cladoxylopsids are a group of plants known only as fossils that are thought to be ancestors of ferns and horsetails.They had a central trunk, from the top of which several lateral branches were attached. Fossils of these plants originate in the Middle Devonian to Early Carboniferous periods ,...
trees grew as a large tree with true wood
Wood
Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...
. These are the oldest known trees of the world's first forests. Prototaxites
Prototaxites
The genus Prototaxites describes terrestrial organisms known only from fossils dating from the Silu-Devonian, approximately 420 to 370 million years ago. Prototaxites formed large trunk-like structures up to wide, reaching in height, made up of interwoven tubes just in diameter...
was the fruiting body of an enormous fungus that stood more than 8 meter tall. By the end of the Devonian, the first seed-forming plants had appeared. This rapid appearance of so many plant groups and growth forms has been called the "Devonian Explosion". The primitive arthropods co-evolved with this diversified terrestrial vegetation structure. The evolving co-dependence of insects and seed-plants that characterizes a recognizably modern world had its genesis in the late Devonian. The development of soils and plant root systems probably led to changes in the speed and pattern of erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
and sediment deposition.
The 'greening' of the continents acted as a carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
sink
Carbon dioxide sink
A carbon sink is a natural or artificial reservoir that accumulates and stores some carbon-containing chemical compound for an indefinite period. The process by which carbon sinks remove carbon dioxide from the atmosphere is known as carbon sequestration...
, and atmospheric
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
levels of this greenhouse gas
Greenhouse gas
A greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...
may have dropped. This may have cooled the climate and led to a massive extinction event
Extinction event
An extinction event is a sharp decrease in the diversity and abundance of macroscopic life. They occur when the rate of extinction increases with respect to the rate of speciation...
. see Late Devonian extinction
Late Devonian extinction
The Late Devonian extinction was one of five major extinction events in the history of the Earth's biota. A major extinction, the Kellwasser Event, occurred at the boundary that marks the beginning of the last phase of the Devonian period, the Famennian faunal stage, , about 374 million years ago...
.
Also in the Devonian, both vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
s and arthropods were solidly established on the land.
CarboniferousCarboniferousThe Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
Flora
The main Early Carboniferous plants were the Equisetales
Equisetales
The Equisetales is an order of pteridophytes with only one living genus Equisetum , of the family Equisetaceae. The fossil record includes additional extinct species in the Equisetaceae and the extinct families Calamitaceae and Archaeocalamitaceae....
(Horse-tails), Sphenophyllales
Sphenophyllum
Sphenophyllum is a genus in the order Sphenophyllales....
(scrambling plants), Lycopodiales (Club mosses), Lepidodendrales
Lepidodendrales
Lepidodendrales were primitive, vascular, arborescent plants related to the lycopsids . They thrived during the Carboniferous period, and some reached heights of over 30 meters, with trunks often more than one meter in diameter...
(scale trees), Filicales (Ferns), Medullosales
Medullosales
The Medullosales is an order of pteridospermous seed plants characterised by large radiospermic ovules with a vascularised nucellus, complex pollen-organs, stems and rachises with a dissected stele, and frond-like leaves. Their nearest still-living relatives are probably the cycads.Most...
(previously included in the "seed ferns
Pteridospermatophyta
The term Pteridospermatophyta refers to several distinct groups of extinct seed-bearing plants . The oldest fossil evidence of plants of this type is of late Devonian age, and they flourished particularly during the Carboniferous and Permian periods...
", an artificial assemblage of a number of early gymnosperm
Gymnosperm
The gymnosperms are a group of seed-bearing plants that includes conifers, cycads, Ginkgo, and Gnetales. The term "gymnosperm" comes from the Greek word gymnospermos , meaning "naked seeds", after the unenclosed condition of their seeds...
groups) and the Cordaitales
Cordaitales
Cordaitales is an extinct order of primitive conifers....
. These continued to dominate throughout the period, but during late Carboniferous
Pennsylvanian
The Pennsylvanian is, in the ICS geologic timescale, the younger of two subperiods of the Carboniferous Period. It lasted from roughly . As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain...
, several other groups, Cycadophyta (cycads), the Callistophytales
Callistophytales
The Callistophytales was an order of mainly scrambling and lianescent plants found in the wetland "coal swamps" of Euramerica and Cathaysia. They were characterised by having bilaterally-symmetrical, non-cupulate ovules attached to the underside of pinnules that were morphologically similar to the...
(another group of "seed ferns"), and the Voltziales
Voltziales
Voltziales is an extinct order related to modern conifers....
(related to and sometimes included under the conifers), appeared.
The Carboniferous lycophytes of the order Lepidodendrales, which are cousins (but not ancestors) of the tiny club-moss of today, were huge trees with trunks 30 meters high and up to 1.5 meters in diameter. These included Lepidodendron
Lepidodendron
Lepidodendron is an extinct genus of primitive, vascular, arborescent plant related to the Lycopsids . It was part of the coal forest flora. They sometimes reached heights of over , and the trunks were often over in diameter, and thrived during the Carboniferous period...
(with its fruit cone called Lepidostrobus), Halonia, Lepidophloios and Sigillaria
Sigillaria
Sigillaria is a genus of extinct, spore-bearing, arborescent plants which flourished in the Late Carboniferous period but dwindled to extinction in the early Permian period. It was a lycopodiophyte, and is related to the lycopsids, or club-mosses, but even more closely to quillworts, as was its...
. The roots of several of these forms are known as Stigmaria
Stigmaria
Stigmaria are a type of branching tree root fossil found in Carboniferous rocks. They were the roots of coal forest lycopsid trees such as Sigillaria and Lepidodendron. Each trunk tended to have four of those roots. Stigmaria is a form taxon, as the genus and species of the plant bearing the root...
.
The fronds of some Carboniferous ferns are almost identical with those of living species. Probably many species were epiphytic. Fossil ferns and "seed ferns" include Pecopteris
Pecopteris
Pecopteris was a form genus of leaves from several unrelated plant groups that flourished the early Carboniferous period and on to c. 250 Ma. Pecopteris first appeared in the Devonian period, but flourished in the Carboniferous, especially the Pennsylvanian...
, Cyclopteris, Neuropteris
Neuropteris
Neuropteris is an extinct seed fern that existed in the Carboniferous period, known only from fossils.Major species include Neuropteris loschi....
, Alethopteris
Alethopteris
Alethopteris is an genus of fossil seed ferns that existed in the Carboniferous period ....
, and Sphenopteris; Megaphyton and Caulopteris were tree ferns.
The Equisetales included the common giant form Calamites
Calamites
Calamites is a genus of extinct arborescent horsetails to which the modern horsetails are closely related. Unlike their herbaceous modern cousins, these plants were medium-sized trees, growing to heights of more than 30 meters...
, with a trunk diameter of 30 to 60 cm and a height of up to 20 meters. Sphenophyllum
Sphenophyllum
Sphenophyllum is a genus in the order Sphenophyllales....
was a slender climbing plant with whorls of leaves, which was probably related both to the calamites and the lycopods.
Cordaites
Cordaites
Cordaites is an important genus of extinct gymnosperms which grew on wet ground similar to the Everglades in Florida. Brackish water mussels and crustacea are found frequently between the roots of these trees. The fossils are found in rock sections from the Upper Carboniferous of the Dutch -...
, a tall plant (6 to over 30 meters) with strap-like leaves, was related to the cycads and conifers; the catkin
Catkin
A catkin or ament is a slim, cylindrical flower cluster, with inconspicuous or no petals, usually wind-pollinated but sometimes insect pollinated . They contain many, usually unisexual flowers, arranged closely along a central stem which is often drooping...
-like inflorescence, which bore yew-like berries, is called Cardiocarpus. These plants were thought to live in swamps and mangroves. True coniferous trees (Walchia
Walchia
Walchia is a fossil conifer, cypress-like genus of Upper Pennsylvanian and lower Permian . It is found in Europe; also North America...
, of the order Voltziales) appear later in the Carboniferous, and preferred higher drier ground.
PermianPermianThe PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
flora
The Permian began with the Carboniferous flora still flourishing. About the middle of the Permian there was a major transition in vegetation. The swamp-loving lycopod trees of the Carboniferous, such as LepidodendronLepidodendron
Lepidodendron is an extinct genus of primitive, vascular, arborescent plant related to the Lycopsids . It was part of the coal forest flora. They sometimes reached heights of over , and the trunks were often over in diameter, and thrived during the Carboniferous period...
and Sigillaria
Sigillaria
Sigillaria is a genus of extinct, spore-bearing, arborescent plants which flourished in the Late Carboniferous period but dwindled to extinction in the early Permian period. It was a lycopodiophyte, and is related to the lycopsids, or club-mosses, but even more closely to quillworts, as was its...
, were replaced by the more advanced conifers, which were better adapted to the changing climatic conditions. Lycopods and swamp forests still dominated the South China
South China (continent)
South China continent, also known as South China craton, South Chinese craton, or Yangtze craton, was an ancient continent that contained today's South and Southeast China , Indochina, and parts of Southeast Asia...
continent because it was an isolated continent and it sat near or at the equator. Oxygen levels were probably high there. The Permian saw the radiation of many important conifer groups, including the ancestors of many present-day families. The ginkgo
Ginkgo
Ginkgo , also spelled gingko and known as the Maidenhair Tree, is a unique species of tree with no close living relatives...
s and cycads also appeared during this period. Rich forests were present in many areas, with a diverse mix of plant groups. The gigantopterid
Gigantopterid
Gigantopterids is the name given to fossils of a group of plants existing in the Late Permian, some . Gigantopterids were among the most advanced land plants of the Paleozoic and disappeared soon after the massive Permian–Triassic extinction event...
s thrived during this time; some of these may have been part of the ancestral flowering plant
Flowering plant
The flowering plants , also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants. Angiosperms are seed-producing plants like the gymnosperms and can be distinguished from the gymnosperms by a series of synapomorphies...
lineage, though flowers evolved only considerably later.
TriassicTriassicThe Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
flora
On land, the holdover plants included the lycophytes, the dominant cycadCycad
Cycads are seed plants typically characterized by a stout and woody trunk with a crown of large, hard and stiff, evergreen leaves. They usually have pinnate leaves. The individual plants are either all male or all female . Cycads vary in size from having a trunk that is only a few centimeters...
s, ginkgophyta (represented in modern times by Ginkgo biloba
Ginkgo
Ginkgo , also spelled gingko and known as the Maidenhair Tree, is a unique species of tree with no close living relatives...
) and glossopterid
Glossopteridales
Glossopteridales is an extinct order of plants belonging to Pteridospermatophyta, or Seed Ferns. They arose at the beginning of the Permian on the southern continent of Gondwana, but dwindled to extinction by the end of the Permian period . The best known genus is Glossopteris.- External links :*...
s. The spermatophyte
Spermatophyte
The spermatophytes comprise those plants that produce seeds. They are a subset of the embryophytes or land plants...
s, or seed plants came to dominate the terrestrial flora: in the northern hemisphere, conifers flourished. Dicroidium
Dicroidium
Dicroidium is an extinct genus of fork-leaved seed ferns that were distributed over Gondwana during the Triassic . Their fossils are known from South Africa, Australia, New Zealand, South America and Antarctica...
(a seed fern) was the dominant southern hemisphere tree during the Early Triassic period.
JurassicJurassicThe Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
flora
The arid, continental conditions characteristic of the Triassic steadily eased during the Jurassic period, especially at higher latitudes; the warm, humid climate allowed lush jungles to cover much of the landscape. Conifers dominated the flora, as during the Triassic; they were the most diverse group and constituted the majority of large trees. Extant conifer families that flourished during the Jurassic included the AraucariaceaeAraucariaceae
Araucariaceae, commonly referred to as araucarians, is a very ancient family of coniferous trees. It achieved its maximum diversity in the Jurassic and Cretaceous periods, when it was distributed almost worldwide...
, Cephalotaxaceae
Cephalotaxaceae
The family Cephalotaxaceae is a small grouping of conifers, with three genera and about 20 species, closely allied to the Taxaceae, and included in that family by some botanists. They are restricted to east Asia, except for two species of Torreya found in the southwest and southeast of the USA;...
, Pinaceae
Pinaceae
Pinaceae are trees or shrubs, including many of the well-known conifers of commercial importance such as cedars, firs, hemlocks, larches, pines and spruces. The family is included in the order Pinales, formerly known as Coniferales. Pinaceae are supported as monophyletic by its protein-type sieve...
, Podocarpaceae
Podocarpaceae
Podocarpaceae is a large family of mainly Southern Hemisphere conifers, comprising about 156 species of evergreen trees and shrubs. It contains 19 genera if Phyllocladus is included and if Manoao and Sundacarpus are recognized....
, Taxaceae
Taxaceae
The family Taxaceae, commonly called the yew family, includes three genera and about 7 to 12 species of coniferous plants, or in other interpretations , six genera and about 30 species....
and Taxodiaceae
Taxodiaceae
The Taxodiaceae were at one time regarded as a distinct plant family comprising the following ten genera of coniferous trees:*Athrotaxis*Cryptomeria*Cunninghamia*†Cunninghamites*Glyptostrobus*Metasequoia*Sciadopitys...
. The extinct Mesozoic conifer family Cheirolepidiaceae
Cheirolepidiaceae
Cheirolepidiaceae is a family of extinct coniferous plants.This family of conifers, superficially similar to Cupressaceae, was a significant part of the flora of the Mesozoic, around . They are united by the possession of a distinctive pollen type assigned to the form genus Classopollis...
dominated low latitude vegetation, as did the shrubby Bennettitales
Bennettitales
Bennettitales is an extinct order of seed plants that first appeared in the Triassic period and became extinct toward the end of the Cretaceous...
. Cycad
Cycad
Cycads are seed plants typically characterized by a stout and woody trunk with a crown of large, hard and stiff, evergreen leaves. They usually have pinnate leaves. The individual plants are either all male or all female . Cycads vary in size from having a trunk that is only a few centimeters...
s were also common, as were ginkgo
Ginkgo
Ginkgo , also spelled gingko and known as the Maidenhair Tree, is a unique species of tree with no close living relatives...
s and tree ferns in the forest. Smaller fern
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
s were probably the dominant undergrowth. Caytoniaceous seed ferns were another group of important plants during this time and are thought to have been shrub to small-tree sized. Ginkgo-like plants were particularly common in the mid- to high northern latitudes. In the Southern Hemisphere, podocarps were especially successful, while Ginkgos and Czekanowskiales were rare.
CretaceousCretaceousThe Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
flora
Campanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...
). Their evolution was aided by the appearance of bee
Bee
Bees are flying insects closely related to wasps and ants, and are known for their role in pollination and for producing honey and beeswax. Bees are a monophyletic lineage within the superfamily Apoidea, presently classified by the unranked taxon name Anthophila...
s; in fact angiosperms and insects are a good example of coevolution. The first representatives of many modern trees, including fig
Ficus
Ficus is a genus of about 850 species of woody trees, shrubs, vines, epiphytes, and hemiepiphyte in the family Moraceae. Collectively known as fig trees or figs, they are native throughout the tropics with a few species extending into the semi-warm temperate zone. The Common Fig Ficus is a genus of...
s, planes
Platanus
Platanus is a small genus of trees native to the Northern Hemisphere. They are the sole living members of the family Platanaceae....
and magnolia
Magnolia
Magnolia is a large genus of about 210 flowering plant species in the subfamily Magnolioideae of the family Magnoliaceae. It is named after French botanist Pierre Magnol....
s, appeared in the Cretaceous. At the same time, some earlier Mesozoic gymnosperm
Gymnosperm
The gymnosperms are a group of seed-bearing plants that includes conifers, cycads, Ginkgo, and Gnetales. The term "gymnosperm" comes from the Greek word gymnospermos , meaning "naked seeds", after the unenclosed condition of their seeds...
s, like Conifers continued to thrive, although other taxa like Bennettitales
Bennettitales
Bennettitales is an extinct order of seed plants that first appeared in the Triassic period and became extinct toward the end of the Cretaceous...
died out before the end of the period.
Cenozoic flora
The Cenozoic is just as much the age of savannas, or the age of co-dependent flowering plants and insects. At 35 Ma, grasses evolved from among the angiosperms.About ten thousand years ago, humans in the Fertile Crescent
Fertile Crescent
The Fertile Crescent, nicknamed "The Cradle of Civilization" for the fact the first civilizations started there, is a crescent-shaped region containing the comparatively moist and fertile land of otherwise arid and semi-arid Western Asia. The term was first used by University of Chicago...
of the Middle East develop agriculture. Plant domestication begins with cultivation of Neolithic
Neolithic
The Neolithic Age, Era, or Period, or New Stone Age, was a period in the development of human technology, beginning about 9500 BC in some parts of the Middle East, and later in other parts of the world. It is traditionally considered as the last part of the Stone Age...
founder crops. This process of food production, coupled later with the domestication of animals caused a massive increase in human population that has continued to the present. In Jericho (modern Israel), there is a settlement with about 19,000 people. At the same time, Sahara is green with rivers, lakes, cattles, crocodiles and monsoons.
At 8 ka, Common (Bread) wheat (Triticum aestivum) originates in southwest Asia due to hybridisation of emmer wheat with a goat-grass, Aegilops tauschii.
At 6.5 ka, two rice species are domesticated: Asian rice, Oryza sativa
Oryza sativa
Oryza sativa, commonly known as Asian rice, is the plant species most commonly referred to in English as rice. Oryza sativa is the cereal with the smallest genome, consisting of just 430Mb across 12 chromosomes...
, and African rice Oryza glaberrima.
Species Differentiation
- Development of rootRootIn vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...
ed plants - Flowering plants vs. Conifers
- FernFernA fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
s and other primitive plants - Borderline species such as coliform protistProtistProtists are a diverse group of eukaryotic microorganisms. Historically, protists were treated as the kingdom Protista, which includes mostly unicellular organisms that do not fit into the other kingdoms, but this group is contested in modern taxonomy...
s
See also
- PlantPlantPlants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
- FloraFloraFlora is the plant life occurring in a particular region or time, generally the naturally occurring or indigenous—native plant life. The corresponding term for animals is fauna.-Etymology:...
- PaleobotanyPaleobotanyPaleobotany, also spelled as palaeobotany , is the branch of paleontology or paleobiology dealing with the recovery and identification of plant remains from geological contexts, and their use for the biological reconstruction of past environments , and both the evolutionary history of plants, with a...
- Plant evolutionary developmental biologyPlant evolutionary developmental biologyEvolutionary developmental biology refers to 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...
- Evolutionary history of plantsEvolutionary history of plantsThe evolution of plants has resulted in increasing levels of complexity, from the earliest algal mats, through bryophytes, lycopods, ferns to the complex gymnosperms and angiosperms of today...
- Timeline of evolutionTimeline of evolutionThis timeline of evolution of life outlines the major events in the development of life on planet Earth since it first originated until the present day. In biology, evolution is any change across successive generations in the heritable characteristics of biological populations...
External links
- Interactive Plant Evolution Timeline - from the University of Cambridge Ensemble Project