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Land plant phyla

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The ten Divisions into which plants, here defined as living (extant) land plants, may be placed are shown in the table below. This definition excludes the algal Divisions Chlorophyta and Charophyta which are included in the clade Viridiplantae (see also current definitions of Plantae).

The definition and classification of plants at this level varies from source to source. Thus some sources place horsetails in division Arthrophyta and ferns in division Pteridophyta,[14] while others place them both in Pteridophyta, as shown below. The division Pinophyta may be used for all gymnosperms (i.e. including cycads, ginkgos and gnetophytes),[15] or for conifers alone as below.

Since the first publication of the APG system in 1998, which proposed a classification of angiosperms to the level of orders, many sources have preferred to treat ranks higher than orders as informal clades. Where formal ranks have been provided, the traditional divisions listed below have been reduced to a very much lower level, e.g. subclasses.

Anthophyta. The anthophytes were thought to be a clade comprising plants bearing flower-like structures.

Anthophyta

Cycad. Cycads are gymnosperms (naked seeded), meaning their unfertilized seeds are open to the air to be directly fertilized by pollination, as contrasted with angiosperms, which have enclosed seeds with more complex fertilization arrangements.

Cycad

Cycads have very specialized pollinators, usually a specific species of beetle. They have been reported to fix nitrogen in association with a cyanobacterium living in the roots. These blue-green algae produce a neurotoxin called BMAA that is found in the seeds of cycads. This neurotoxin may enter a human food chain as the cycad seeds may be eaten by bats, and humans may eat the bats. It is hypothesized that this is a source of some neurological diseases in humans.[3] Origins[edit] Taxonomy[edit] The number of species in the clade is low compared to the number in most other plant phyla.

The number of described cycad species has doubled in the past 25 years, mostly due to improved sampling and further exploration. Suborder Cycadineae Family Cycadaceae. Flowering plant. The ancestors of flowering plants diverged from gymnosperms around 245–202 million years ago, and the first flowering plants known to exist are from 160 million years ago.

Flowering plant

They diversified enormously during the Lower Cretaceous and became widespread around 120 million years ago, but replaced conifers as the dominant trees only around 60–100 million years ago. Angiosperm derived characteristics[edit] Ginkgoales. Gnetophyta. Welwitschia mirabilis male cones Ephedra distachya (male flowers) Ephedra distachya (female plant in bloom) Gnetum gnemon male Gnetum gnemon female.

Gnetophyta

Hornwort. This article is about the non-vascular plants.

Hornwort

Lycopodiophyta. The Division Lycopodiophyta (sometimes called Lycophyta or Lycopods) is a tracheophyte subdivision of the Kingdom Plantae.

Lycopodiophyta

It is the oldest extant (living) vascular plant division at around 410 million years old,[4]:99 and it includes some of the most "primitive" extant species. Marchantiophyta. The Marchantiophyta i/mɑrˌkæntiˈɒfɨtə/ are a division of non-vascular bryophyte land plants commonly referred to as hepatics or liverworts.

Marchantiophyta

Like other bryophytes, they have a gametophyte-dominant life cycle, in which cells of the plant carry only a single set of genetic information. Liverworts are typically small, usually from 2–20 mm wide with individual plants less than 10 cm long, and are therefore often overlooked. However, certain species may cover large patches of ground, rocks, trees or any other reasonably firm substrate on which they occur.

They are distributed globally in almost every available habitat, most often in humid locations although there are desert and arctic species as well. Physical characteristics[edit] Description[edit] Moss. Mosses are commonly confused with lichens, hornworts, and liverworts.[4] Lichens may superficially look like mosses, and have a common names that includes the word "moss" (e.g., "reindeer moss" or "iceland moss"), but are not related to mosses.[4]:3 Mosses, hornworts, and liverworts are collectively called "bryophytes".

Moss

Bryophytes share the properties of not having vascular tissue and producing spores instead of flowers and seeds. Bryohpytes have the haploid gametophyte generation as the dominant phase of the life cycle. Pinophyta. Although the total number of species is relatively small, conifers are of immense ecological importance.

Pinophyta

They are the dominant plants over huge areas of land,[4] most notably the boreal forests of the northern hemisphere,[1] but also in similar cool climates in mountains further south. Boreal conifers have many wintertime adaptations. The narrow conical shape of northern conifers, and their downward-drooping limbs, help them shed snow. Many of them seasonally alter their biochemistry to make them more resistant to freezing, called "hardening". While tropical rainforests have more biodiversity and turnover, the immense conifer forests of the world represent the largest terrestrial carbon sink, i.e. where carbon from atmospheric CO2 is bound as organic compounds.

Pteridophyte. Pteridophytes or Pteridophyta, in the broad interpretation of the term (or sensu lato), are vascular plants (plants with xylem and phloem) that reproduce and disperse via spores.

Pteridophyte

Because they produce neither flowers nor seeds, they are referred to as cryptogams. The group includes ferns, horsetails, clubmosses, spikemosses and quillworts. These do not form a monophyletic group, because ferns and horsetails are more closely related to seed plants than to lycophytes (clubmosses, spikemosses and quillworts). Therefore, pteridophytes are no longer considered to form a valid taxon, but the term is still used as an informal way to refer to ferns (monilophytes) and lycophytes, and some recent authors have used the term to refer strictly to the monilophytes.

Pteridophyte classification[edit] In addition to these living groups, several groups that are now extinct and known only from fossils are considered to belong to pteridophytes.