Ginkgo is a genus of highly unusual non-flowering plants with one extant species, G. biloba Ginkgo , also known as the Maidenhair Tree after Adiantum, is a unique species of tree with no close living relatives. The ginkgo is classified in its own division, the Ginkgophyta, comprising the single class Ginkgoopsida, order Ginkgoales, family Ginkgoaceae, genus Ginkgo and is the only extant species within this group. It is one of the best-, which is regarded as a living fossil Living fossil is an informal term for any living species of organism which appears to be the same as a species otherwise only known from fossils and which has no close living relatives. These species have all survived major extinction events, and generally retain low taxonomic diversities. A species which successfully radiates (forming many new.
Prehistory
The Ginkgo is a living fossil Living fossil is an informal term for any living species of organism which appears to be the same as a species otherwise only known from fossils and which has no close living relatives. These species have all survived major extinction events, and generally retain low taxonomic diversities. A species which successfully radiates (forming many new, with fossils recognisably related to modern Ginkgo from the Permian The Permian[note 1] is a geologic period and system characterized among land vertebrates by the diversification of the early amniotes into the ancestral groups of the mammals, turtles, lepidosaurs and archosaurs. The Permian Period follows the Carboniferous and extends from 299.0 ± 0.8 to 251.0 ± 0.4 Ma . It is the last period of the Paleozoic, dating back 270 million years. The most plausible ancestral group for the order Ginkgoales is the Pteridospermatophyta, also known as the "seed ferns The term Pteridospermatophyta refers to several distinct groups of extinct spermatophyte of the Plantae kingdom. Members of this division first appeared in late Devonian times, and flourished during Carboniferous and Permian times. They declined during the Mesozoic Era and had mostly disappeared by the end of the Cretaceous Period, though fossil," specifically the order Peltaspermales. The closest living relatives of the clade are the cycads,[3] which share with the extant G. biloba the characteristic of motile sperm. Fossils attributable to the genus Ginkgo first appeared in the Early Jurassic The Early Jurassic epoch is the earliest of three epochs of the Jurassic period. The Early Jurassic starts immediately after the Triassic-Jurassic extinction event (199.6 Ma (million years ago) and ends at the start of the Middle Jurassic (175.6 Ma), and the genus diversified and spread throughout Laurasia Laurasia was a supercontinent that most recently existed as a part of the split of the Pangaea supercontinent in the late Mesozoic era. It was located in the north after Pangaea split into two followed by Gondwanaland in the south. It included most of the landmasses which make up today's continents of the northern hemisphere, chiefly Laurentia ( during the middle Jurassic The Jurassic is a geologic period and system that extends from about 199.6± 0.6 Ma to 145.5± 4 Ma, 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 the major Triassic– and Early Cretaceous The Early Cretaceous or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 146 Ma to 100 Ma. It declined in diversity as the Cretaceous progressed, and by the Paleocene The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about 65.5 to 56 million years ago . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era. As with most other older geologic periods, the strata that define the epoch's beginning and end are well identified but the exact date of the, Ginkgo adiantoides was the only Ginkgo species left in the Northern Hemisphere The Northern Hemisphere is the half of a planet that is north of equator—the word hemisphere literally means 'half sphere'. It is also that half of the celestial sphere north of the celestial equator. Earth's northern hemisphere contains most of its land area and most of its human population while a markedly different (and poorly documented) form persisted in the Southern Hemisphere The Southern Hemisphere is the half of a planet that is south of the equator—the word hemisphere (from the Greek word σφαιρα +ημι(half)) literally means 'half ball'. It is also that half of the celestial sphere south of the celestial equator. At the end of the Pliocene The Pliocene Epoch (spelled Pleiocene in older texts) is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present, Ginkgo fossils disappeared from the fossil record everywhere except in a small area of central China where the modern species survived. It is doubtful whether the Northern Hemisphere fossil species of Ginkgo can be reliably distinguished. Given the slow pace of evolution and morphological similarity between members of the genus, there may have been only one or two species existing in the Northern Hemisphere through the entirety of the Cenozoic The Cenozoic Era is the most recent of the three classic geological eras and covers the period from 65.5 million years ago to the present. It is marked by the Cretaceous–Tertiary extinction event at the end of the Cretaceous that saw the demise of the last non-avian dinosaurs and the end of the Mesozoic Era. The Cenozoic era is ongoing: present-day G. biloba (including G. adiantoides) and G. gardneri from the Paleocene The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about 65.5 to 56 million years ago . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era. As with most other older geologic periods, the strata that define the epoch's beginning and end are well identified but the exact date of the of Scotland Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the southwest. In addition to the mainland, Scotland.[4]
Fossil Ginkgo huttonii leaves from the Jurassic of EnglandAt least morphologically, G. gardneri and the Southern Hemisphere species are the only known post-Jurassic taxa that can be unequivocally recognised. The remainder may have been ecotypes In evolutionary ecology, an ecotype describes a genetically distinct geographic variety, population or race within species (or among closely related), which is adapted to specific environmental conditions. Typically, ecotypes exhibit phenotypic differences (such as in morphology or physiology) stemming from environmental heterogeneity and are or subspecies Subspecies in biological classification, is either a taxonomic rank subordinate to species, or a taxonomic unit in that rank (plural: subspecies). A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one. The implications would be that G. biloba had occurred over an extremely wide range, had remarkable genetic flexibility and, though evolving Evolution is the change in the inherited traits of a population of organisms through successive generations. This change results from interactions between processes which introduce variation into a population, and other processes which remove it. As a result, variants with particular traits become more, or less, common. A trait is a particular genetically, never showed much speciation Speciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages. Whether genetic drift is a minor or major contributor to. While it may seem improbable that a species may exist as a contiguous entity for many millions of years, many of the Ginkgo's life-history parameters fit. These are: extreme longevity; slow reproduction rate; (in Cenozoic and later times) a wide, apparently contiguous, but steadily contracting distribution coupled with, as far as can be demonstrated from the fossil record, extreme ecological conservatism (restriction to disturbed streamside environments).[5]
Modern-day G. biloba grows best in environments that are well-watered and drained,[6] and the extremely similar fossil Ginkgo favored similar environments: the sediment record at the majority of fossil Ginkgo localities indicates it grew primarily in disturbed environments along streams and levees.[5] Ginkgo therefore presents an "ecological paradox" because while it possesses some favorable traits for living in disturbed environments (clonal reproduction) many of its other life-history traits (slow growth, large seed size, late reproductive maturity) are the opposite of those exhibited by modern plants that thrive in disturbed settings.[7]
Given the slow rate of evolution of the genus, it is possible that Ginkgo represents a pre-angiosperm The flowering plants , also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants. Together with gymnosperms, they are the only extant groups of seed-producing plants, but they can be distinguished from the gymnosperms by a series of synapomorphies (derived characteristics). These characteristics include flowers, strategy for survival in disturbed streamside environments. Ginkgo evolved in an era before flowering plants, when ferns A fern is any one of a group of about 12,000 species of plants. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants. Ferns do not have either seeds or flowers (they reproduce via spores), cycads Cycads are seed plants characterized by a large crown of compound leaves and a stout trunk. They are evergreen, dioecious plants having large pinnately compound leaves. They are frequently confused with and mistaken for palms or ferns, but are only distantly related to both, and instead belong to the division Cycadophyta, and cycadeoids Bennettitales is an extinct order of seed plants that first appeared in the Triassic period and became extinct toward the end of the Cretaceous. Some were characterized by thick trunks and pinnately compound leaves that bore a superficial resemblance to those of cycads, differing primarily in stomatal arrangement dominated disturbed streamside environments, forming a low, open, shrubby canopy. Ginkgo's large seeds and habit of "bolting" - growing to a height of 10 m before elongating its side branches - may be adaptions to such an environment. The fact that diversity in the genus Ginkgo drops through the Cretaceous (along with that of ferns, cycads, and cycadeoids) at the same time that flowering plants were on the rise, supports the notion that flowering plants with better adaptations to disturbance displaced Ginkgo and its associates over time.[8]
Ginkgo has been used for classifying plants with leaves In botany, a leaf is an above-ground plant organ specialized for photosynthesis. For this purpose, a leaf is typically flat and thin. As an evolutionary trait, the flatness of leaves works to expose the chloroplasts to more light and to increase the absorption of carbon dioxide at the expense of water loss. In the Devonian period, when carbon that have more than four veins In botany, a leaf is an above-ground plant organ specialized for photosynthesis. For this purpose, a leaf is typically flat and thin. As an evolutionary trait, the flatness of leaves works to expose the chloroplasts to more light and to increase the absorption of carbon dioxide at the expense of water loss. In the Devonian period, when carbon per segment, while Baiera for those with less than four veins per segment. Sphenobaiera has been used to classify plants with a broadly wedge-shaped leaf that lacks a distinct leaf stem. Trichopitys is distinguished by having multiple-forked leaves with cylindrical (not flattened) thread-like ultimate divisions; it is one of the earliest fossils ascribed to the Ginkgophyta.
References
- ^ Taylor, Thomas N.; Edith L. Taylor (1993). The Biology and Evolution of Fossil Plants. Englewood Cliffs, NJ: Prentice Hall. pp. 138, 197. ISBN The International Standard Book Number is a unique numeric commercial book identifier based upon the 9-digit Standard Book Numbering (SBN) code created by Gordon Foster, now Emeritus Professor of Statistics at Trinity College, Dublin, for the booksellers and stationers W.H. Smith and others in 1966 0-13-651589-4.
- ^ "Genus: Ginkgo L.". Germplasm Resources Information Network (GRIN). United States Department of Agriculture, Agricultural Research Service, Beltsville Area. http://www.ars-grin.gov/cgi-bin/npgs/html/genus.pl?4960. Retrieved 2008-03-26.
- ^ Royer et al., p.84.
- ^ Royer et al., p.85.
- ^ a b Royer et al., p.91.
- ^ Royer et al., p.87.
- ^ Royer et al., p.92.
- ^ Royer et al., p.93.
Sources
- Royer, Dana L.; Hickey, Leo J.; Wing, Scott L. Ecological Conservatism in the "Living Fossil" Ginkgo. Paleobiology, (29)1, 2003, 84-104.
Categories: Gymnosperms
Wed, 23 Jun 2010 20:49:13 GMT+00:00
Schwaebische Post Der Radler-Tross hat einen Namen: Tour Ginkgo . Deren Spenden sollen in diesem Jahr der Stauferklinik zugutekommen, wo Unterkuenfte fuer Eltern geschaffen ...
