Spermatophyte

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Seed plants
Temporal range: Famennian–Present
PinusSylvestris.jpg
Scots pine, Pinus sylvestris , a member of the Pinophyta
Acer pseudoplatanus Chaltenbrunnen.jpg
Sycamore maple, Acer pseudoplatanus , a member of the Eudicots
Scientific classification Red Pencil Icon.png
Kingdom: Plantae
Clade: Tracheophytes
Clade: Spermatophytes
Divisions
Synonyms
  • Phanerogamae
  • Phaenogamae

The spermatophytes (lit.'seed-bearing plants'; from Ancient Greek σπέρματος (spérmatos) 'seed',and φυτόν (phytón) 'plant'), also known as phanerogams (taxon Phanerogamae) or phaenogams (taxon Phaenogamae), comprise those plants that produce seeds, hence the alternative name seed plants. They are a subset of the embryophytes or land plants.

Contents

The term phanerogams or phanerogamae is derived from the Greek φανερός (phanerós), meaning "visible", in contrast to the cryptogamae (from Ancient Greek κρυπτός (kruptós) 'hidden'), together with the suffix γαμέω (gaméō), meaning "to marry". These terms distinguished those plants with hidden sexual organs (cryptogamae) from those with visible sexual organs (phanerogamae).

Description

The extant spermatophytes form five divisions, the first four of which are traditionally grouped as gymnosperms, plants that have unenclosed, "naked seeds": [1] :172

The fifth extant division is the flowering plants, also known as angiosperms or magnoliophytes, the largest and most diverse group of spermatophytes:

In addition to the five living taxa listed above, the fossil record contains evidence of many extinct taxa of seed plants, among those:

By the Triassic period, seed ferns had declined in ecological importance, and representatives of modern gymnosperm groups were abundant and dominant through the end of the Cretaceous, when the angiosperms radiated.

Evolutionary history

A whole genome duplication event in the ancestor of seed plants occurred about 319  million years ago. [2] This gave rise to a series of evolutionary changes that resulted in the origin of seed plants.

A middle Devonian (385-million-year-old) precursor to seed plants from Belgium has been identified predating the earliest seed plants by about 20 million years. Runcaria , small and radially symmetrical, is an integumented megasporangium surrounded by a cupule. The megasporangium bears an unopened distal extension protruding above the mutlilobed integument. It is suspected that the extension was involved in anemophilous (wind) pollination. Runcaria sheds new light on the sequence of character acquisition leading to the seed. Runcaria has all of the qualities of seed plants except for a solid seed coat and a system to guide the pollen to the seed. [3]

Relationships and nomenclature

Seed-bearing plants are a subclade of the vascular plants (tracheophytes) and were traditionally divided into angiosperms, or flowering plants, and gymnosperms, which includes the gnetophytes, cycads, ginkgo, and conifers. Older morphological studies believed in a close relationship between the gnetophytes and the angiosperms, [4] in particular based on vessel elements. However, molecular studies (and some more recent morphological [5] [6] and fossil [7] papers) have generally shown a clade of gymnosperms, with the gnetophytes in or near the conifers. For example, one common proposed set of relationships is known as the gne-pine hypothesis and looks like: [8] [9] [10]

angiosperms (flowering plants)

gymnosperms

cycads [11]

Ginkgo

Pinaceae (the pine family)

gnetophytes

other conifers

However, the relationships between these groups should not be considered settled. [4] [12]

Other classifications group all the seed plants in a single division, with classes for the five groups:

A more modern classification ranks these groups as separate divisions (sometimes under the Superdivision Spermatophyta):

An alternative phylogeny of spermatophytes based on the work by Novíkov & Barabaš-Krasni 2015 [13] with plant taxon authors from Anderson, Anderson & Cleal 2007 [14] showing the relationship of extinct clades.

Spermatophytina

Moresnetiopsida Doweld 2001

Lyginopteridopsida Novák 1961 emend. Anderson, Anderson & Cleal 2007

Pachytestopsida Doweld 2001

Callistophytales Rothwell 1981 emend. Anderson, Anderson & Cleal 2007

Peltaspermopsida Doweld 2001

Umkomasiales Doweld 2001

Phasmatocycadopsida Doweld 2001

Pentoxylopsida Pant ex Doweld 2001

Dictyopteridiopsida Doweld 2001

Cycadeoideopsida Scott 1923

Caytoniopsida Thomas ex Frenguelli 1946

Magnoliopsida (Flowering plants)

Acrogymnospermae

Cycadopsida (Cycads)

Ginkgoopsida (Maidenhair trees)

Pinopsida (Conifers)

Unassigned spermatophytes:[ citation needed ]

Related Research Articles

The anthophytes are a grouping of plant taxa bearing flower-like reproductive structures. They were formerly thought to be a clade comprising plants bearing flower-like structures. The group contained the angiosperms - the extant flowering plants, such as roses and grasses - as well as the Gnetales and the extinct Bennettitales.

Gametophyte Haploid stage in the life cycle of plants and algae

A gametophyte is one of the two alternating multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has one set of chromosomes. The gametophyte is the sexual phase in the life cycle of plants and algae. It develops sex organs that produce gametes, haploid sex cells that participate in fertilization to form a diploid zygote which has a double set of chromosomes. Cell division of the zygote results in a new diploid multicellular organism, the second stage in the life cycle known as the sporophyte. The sporophyte can produce haploid spores by meiosis that on germination produce a new generation of gametophytes.

Flowering plant Clade of seed plants that produce flowers

Flowering plants include multiple members of the clade Angiospermae, commonly called angiosperms. The term "angiosperm" is derived from the Greek words angeion and sperma ('seed'), and refers to those plants that produce their seeds enclosed within a fruit. They are the most diverse group of land plants with 64 orders, 416 families, approximately 13,000 known genera and 300,000 known species. Angiosperms were formerly called Magnoliophyta.

Pinales Order of seed plants, also known as conifers

The order Pinales in the division Pinophyta, class Pinopsida, comprises all the extant conifers. The distinguishing characteristic is the reproductive structure known as a cone produced by all Pinales. All of the extant conifers, such as cedar, celery-pine, cypress, fir, juniper, larch, pine, redwood, spruce, yew and Araucaria araucana are included here. Some fossil conifers, however, belong to other distinct orders within the division Pinophyta.

Cycad Division of naked seeded dioecious plants

Cycads are seed plants that typically have a stout and woody (ligneous) trunk with a crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, therefore the individual plants of a species are either male or female. Cycads vary in size from having trunks only a few centimeters to several meters tall. They typically grow very slowly and live very long, with some specimens known to be as much as 1,000 years old. Because of their superficial resemblance, they are sometimes mistaken for palms or ferns, but they are not closely related to either group.

Gnetophyta Division of plants containing three genera of gymnosperms

Gnetophyta is a division of plants, grouped within the gymnosperms, that consists of some 70 species across the three relict genera: Gnetum, Welwitschia, and Ephedra. Fossilized pollen attributed to a close relative of Ephedra has been dated as far back as the Early Cretaceous. Though diverse in the Early Cretaceous, only three families, each containing a single genus, are still alive today. The primary difference between gnetophytes and other gymnosperms is the presence of vessel elements, a system of conduits that transport water within the plant, similar to those found in flowering plants. Because of this, gnetophytes were once thought to be the closest gymnosperm relatives to flowering plants, but more recent molecular studies have brought this hypothesis into question.

Gymnosperm Clade of non-flowering, naked-seeded vascular plants

The gymnosperms, also known as Acrogymnospermae, are a group of seed-producing plants that includes conifers, cycads, Ginkgo, and gnetophytes, forming the clade Gymnospermae. The term gymnosperm comes from the composite word in Greek: γυμνόσπερμος, literally meaning 'naked seeds'. The name is based on the unenclosed condition of their seeds. The non-encased condition of their seeds contrasts with the seeds and ovules of flowering plants (angiosperms), which are enclosed within an ovary. Gymnosperm seeds develop either on the surface of scales or leaves, which are often modified to form cones, or solitary as in yew, Torreya, Ginkgo. Gymnosperms show alternation of generations; and have a dominant diploid sporophytic phase, a reduced haploid gametophytic phase which is dependent on the sporophytic phase.

Embryophyte Subclade of green plants, also known as land plants

The Embryophyta, or land plants, are the most familiar group of green plants that comprise vegetation on Earth. Embryophyta is a clade within the Phragmoplastophyta, a larger clade that also includes several groups of green algae including the Charophyceae and Coleochaetales. Within this larger clade the embryophytes are sister to the Zygnematophyceae/Mesotaeniaceae and consist of the bryophytes plus the polysporangiophytes. Living embryophytes therefore include hornworts, liverworts, mosses, lycophytes, ferns, gymnosperms and flowering plants.

<i>Gnetum</i> genus of tropical gymnosperms in the family Gnetaceae

Gnetum is a genus of gymnosperms, the sole genus in the family Gnetaceae and order Gnetales. They are tropical evergreen trees, shrubs and lianas. Unlike other gymnosperms, they possess vessel elements in the xylem. Some species have been proposed to have been the first plants to be insect-pollinated as their fossils occur in association with extinct pollinating scorpionflies. Molecular phylogenies based on nuclear and plastid sequences from most of the species indicate hybridization among some of the Southeast Asian species. Fossil-calibrated molecular-clocks suggest that the Gnetum lineages now found in Africa, South America and Southeast Asia are the result of ancient long-distance dispersal across seawater.

Bennettitales Extinct order of seed plants

Bennettitales is an extinct order of seed plants that first appeared in the Permian period and became extinct in most areas toward the end of the Cretaceous. Bennettitales are among the most common Mesozoic seed plants, and had morphologies including shrub and cycad-like forms. The foliage of bennettitaleans is superficially nearly indistinguishable from that of cycads, but they are distinguished from cycads by their more complex flower-like reproductive organs, at least some of which were likely pollinated by insects.

Welwitschiaceae Family of plants

Welwitschiaceae is a family of plants of the order Gnetales with one living species, Welwitschia mirabilis, found in southwestern Africa. Three fossil genera have been recovered from the Crato Formation – late Aptian strata located in the Araripe Basin in northeastern Brazil, with one of these also being known from the early Late Cretaceous (Cenomanian-Turonian) Akrabou Formation of Morocco.

Double fertilization Complex fertilization mechanism of flowering plants

Double fertilization is a complex fertilization mechanism of flowering plants (angiosperms). This process involves the joining of a female gametophyte with two male gametes (sperm). It begins when a pollen grain adheres to the stigma of the carpel, the female reproductive structure of a flower. The pollen grain then takes in moisture and begins to germinate, forming a pollen tube that extends down toward the ovary through the style. The tip of the pollen tube then enters the ovary and penetrates through the micropyle opening in the ovule. The pollen tube proceeds to release the two sperm in the megagametophyte.

Microspore Small land plant spores that develop into male gametophytes

Microspores are land plant spores that develop into male gametophytes, whereas megaspores develop into female gametophytes. The male gametophyte gives rise to sperm cells, which are used for fertilization of an egg cell to form a zygote. Megaspores are structures that are part of the alternation of generations in many seedless vascular cryptogams, all gymnosperms and all angiosperms. Plants with heterosporous life cycles using microspores and megaspores arose independently in several plant groups during the Devonian period. Microspores are haploid, and are produced from diploid microsporocytes by meiosis.

A strobilus is a structure present on many land plant species consisting of sporangia-bearing structures densely aggregated along a stem. Strobili are often called cones, but some botanists restrict the use of the term cone to the woody seed strobili of conifers. Strobili are characterized by a central axis surrounded by spirally arranged or decussate structures that may be modified leaves or modified stems.

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

Euphyllophyte Clade of vascular plants

The euphyllophytes are a clade of plants within the tracheophytes. The group may be treated as an unranked clade, a division under the name Euphyllophyta or a subdivision under the name Euphyllophytina. The euphyllophytes are characterized by the possession of true leaves ("megaphylls"), and comprise one of two major lineages of extant vascular plants. As shown in the cladogram below, the euphyllophytes have a sister relationship to the lycopodiophytes or lycopsids. Unlike the lycopodiophytes, which consist of relatively few presently living or extant taxa, the euphyllophytes comprise the vast majority of vascular plant lineages that have evolved since both groups shared a common ancestor more than 400 million years ago. The euphyllophytes consist of two lineages, the spermatophytes or seed plants such as flowering plants (angiosperms) and gymnosperms, and the Polypodiophytes or ferns, as well as a number of extinct fossil groups.

<i>Gnetum africanum</i> Species of seed-bearing plant

Gnetum africanum is a vine gymnosperm species found natively throughout tropical Africa. Though bearing leaves, the genus Gnetum are gymnosperms, related to pine and other conifers.

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.

<i>Ginkgo</i> Genus of ancient seed plants with a single surviving species

Ginkgo is a genus of highly unusual non-flowering seed plants. The scientific name is also used as the English name. The order to which it belongs, Ginkgoales, first appeared in the Permian, 270 million years ago, and is now the only living genus within the order. The rate of evolution within the genus has been slow, and almost all its species had become extinct by the end of the Pliocene; the exception is the sole living species, Ginkgo biloba, which is only found in the wild in China, but is cultivated around the world. The relationships between ginkgos and other groups of plants are not fully resolved.

A 20th-century system of plant taxonomy, the Judd system (1999-2016) of plant classification was drawn up by the American botanist Walter S. Judd (1951-) and collaborators, partially based on APG schemes.

References

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  3. "Science Magazine". Runcaria, a Middle Devonian Seed Plant Precursor. American Association for the Advancement of Science. 2011. Retrieved March 22, 2011.
  4. 1 2 Palmer, Jeffrey D.; Soltis, Douglas E.; Chase, Mark W. (2004). "The plant tree of life: an overview and some points of view". American Journal of Botany. 91 (10): 1437–1445. doi: 10.3732/ajb.91.10.1437 . PMID   21652302.
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  8. Chaw, Shu-Miaw; Parkinson, Christopher L.; Cheng, Yuchang; Vincent, Thomas M.; Palmer, Jeffrey D. (2000). "Seed plant phylogeny inferred from all three plant genomes: Monophyly of extant gymnosperms and origin of Gnetales from conifers". Proceedings of the National Academy of Sciences. 97 (8): 4086–4091. Bibcode:2000PNAS...97.4086C. doi: 10.1073/pnas.97.8.4086 . PMC   18157 . PMID   10760277.
  9. Bowe, L. M.; Michelle, L.; Coat, Gwénaële; Claude (2000). "Phylogeny of seed plants based on all three genomic compartments: Extant gymnosperms are monophyletic and Gnetales' closest relatives are conifers". Proceedings of the National Academy of Sciences . 97 (8): 4092–4097. Bibcode:2000PNAS...97.4092B. doi: 10.1073/pnas.97.8.4092 . PMC   18159 . PMID   10760278.
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  11. Chung-Shien Wu, Ya-Nan Wang, Shu-Mei Liu and Shu-Miaw Chaw (2007). "Chloroplast Genome (cpDNA) of Cycas taitungensis and 56 cp Protein-Coding Genes of Gnetum parvifolium: Insights into cpDNA Evolution and Phylogeny of Extant Seed Plants". Molecular Biology and Evolution. 24 (6): 1366–1379. doi: 10.1093/molbev/msm059 . PMID   17383970.CS1 maint: multiple names: authors list (link)
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Bibliography