Timeline of plant evolution

Source: Wikipedia, the free 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, predominantly involving 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.

Earliest plants

In the strictest sense, the name plant refers to those land plants that form the

Klebsormidiophyceae.[1]

cyanobacterium, a photosynthesising prokaryote and a non-photosynthetic eukaryotic organism, producing a lineage of photosynthesizing eukaryotic organisms in marine and freshwater environments. These earliest photosynthesizing single-celled autotrophs evolved into multicellular organisms such as the Charophyta
, a group of freshwater green algae.

Fossil evidence of plants begins around 3000 Ma with indirect evidence of oxygen-producing photosynthesis in the geological record, in the form of chemical and isotopic signatures in rocks and fossil evidence of colonies of cyanobacteria, photosynthesizing

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.

Fossil evidence for cyanobacteria also comes from the presence of stromatolites in the fossil record deep into the Precambrian. Stromatolites are layered structures formed by the trapping, binding, and cementation of sedimentary grains by microbial biofilms, such as those produced by cyanobacteria. The direct evidence for cyanobacteria is less certain than the evidence for their presence as primary producers of atmospheric oxygen. Modern stromatolites containing cyanobacteria can be found on the west coast of Australia and other areas in saline lagoons and in freshwater.

Axis scale: millions of years ago.

Paleozoic flora

Cambrian flora

Early plants were small, unicellular or filamentous, with simple branching. The identification of plant fossils 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 group of calcareous green algae,

land plants with vascular tissues until the mid-Silurian
.

Ordovician flora

The evidence of plant evolution changes dramatically in the Ordovician with the first extensive appearance of

spores, important dispersal units that have hard protective outer coatings which not only allowed their preservation in the fossil record, but also protected them from the UV light, desiccating environment and possible microorganism attack.[4]

Silurian flora

Artist's impression of Cooksonia pertoni

The first fossil records of

lycopods, such as Baragwanathia (originally discovered in Silurian deposits in Victoria, Australia),[9]
had become widespread.

Devonian flora

By the Devonian Period, the colonization of the land by plants was well underway. The

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 relied on arbuscular mycorrhizal symbioses with fungi to provide them with water and mineral nutrients such as phosphorus.[10] [11]They probably spread by a combination of vegetative reproduction
forming clonal colonies, and sexual reproduction via spores and did not grow much more than a few centimeters tall.

By the Late Devonian, forests of large, primitive plants existed:

cladoxylopsid trees had 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 meters 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

atmospheric concentrations of this greenhouse gas may have dropped.[12] This may have cooled the climate and led to a massive extinction event. see Late Devonian extinction
.

Also in the Devonian, both vertebrates and arthropods were solidly established on the land.

Carboniferous flora

Stigmaria, a fossil tree root. Upper Carboniferous of northeastern Ohio.
Upper Carboniferous of Ohio
.

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

conifers
), appeared.

The Carboniferous lycophytes of the order Lepidodendrales, which were cousins (but not ancestors) of the tiny club-mosses of today, were huge trees with trunks 30 meters high and up to 1.5 meters in diameter. These included

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 include Pecopteris and the tree ferns Megaphyton and Caulopteris. Seed ferns or Pteridospermatophyta include Cyclopteris, Neuropteris, Alethopteris, and Sphenopteris.

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 modern horsetails.

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 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

South China continent because it was an isolated continent and it sat near or at the equator. The Permian saw the radiation of many important conifer groups, including the ancestors of many present-day families. The ginkgos and cycads also appeared during this period. Rich forests were present in many areas, with a diverse mix of plant groups. The gigantopterids thrived during this time; some of these may have been part of the ancestral flowering plant
lineage, though flowers evolved only considerably later.

Mesozoic flora

Triassic flora

On land, the holdover plants included the

seed fern
) was the dominant southern hemisphere tree during the Early Triassic period.

Jurassic 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.

podocarps were especially successful, while Ginkgos and Czekanowskiales were rare.[15][17]

Cretaceous flora

Archaeamphora longicervia
, the earliest known carnivorous plant

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).[18] Their evolution was aided by the appearance of bees; in fact angiosperms and insects are a good example of coevolution. The first representatives of many modern trees, including figs, planes and magnolias, appeared in the Cretaceous. At the same time, some earlier Mesozoic gymnosperms, like Conifers continued to thrive, although other taxa like Bennettitales
died out before the end of the period.

Cenozoic flora

The Cenozoic began at the

grasses
evolved from among the angiosperms. 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, cattle, 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.

Species differentiation

See also

References

  1. PMID 29851097
    .
  2. ^
    doi:10.1111/j.1744-7917.2007.00152.x
    .
  3. PMID 10905606
    .
  4. ^
    PMID 20731783.{{cite journal}}: CS1 maint: numeric names: authors list (link
    )
  5. S2CID 206518080. Archived
    (PDF) from the original on 22 September 2017. Retrieved 1 November 2017.
  6. PMID 29542135
    .
  7. ISBN 978-0-231-11161-4
    .
  8. PMID 21665700
  9. doi:10.1098/rstb.1935.0004
    .
  10. S2CID 4319766
    .
  11. ISSN 2041-1723
    .
  12. ISBN 9780199548149
    .
  13. ISBN 0-563-38449-2
    . Page 65.
  14. ISBN 0-226-04155-7
    (paper). Page 349.
  15. ^ a b Behrensmeyer et al., 1992, 352
  16. ^ Behrensmeyer et al., 1992, 353
  17. ^ Haines, 2000.
  18. S2CID 205458714
    .

External links
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