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The order Pinales in the division Pinophyta, class Pinophyta, comprises all the Extant taxon . The distinguishing characteristic is the reproductive structure known as a conifer cone produced by all Pinales. All of the extant conifers, such as Araucaria, Cedrus, Phyllocladus, Cupressus, fir, juniper, kauri, larch, pine, redwood, spruce, and Taxaceae, are included here. Some fossil conifers, however, belong to other distinct orders within the division Pinophyta.
Multiple molecular studies indicate this order being Paraphyly with respect to Gnetophyta, with studies recovering Gnetales as either a sister group to Pinaceae or being more derived than Pinaceae but sister to the rest of the group.
In contrast, Bentham and Hooker (1880) included only three orders in the class Gymnospermeae, by including taxads within Coniferae;
In the Engler system (1903) Gymnospermae is listed as a subdivision ( Unterabteilung) and adopted more of a splitter approach, including extinct taxa, with the following six classes;
During this period, Gorozhankin published his treatise on Gymnosperms (1895), for which he bears the botanical authority for Pinales, Gorozh.. In his classification, Gymnospermae (alternatively named Archespermae) was a class of the division Archegoniatae, divided into subclasses;
A system of two groups was maintained by the most commonly used classification in the twentieth century, the revision of the Engler system by Pilger (1926), who grouped 12 families of the Gymnospermae subdivision into 2 classes;
The treatment of Gymnosperms as two groups, though with varying composition and names, was followed for most of the twentieth century, including the systems of Chamberlain (1935), Benson (1957) and Cronquist system (1960).
In the latter, Cronquist divided Gymnospermae into two divisions;
Benson,(1957) who introduced the term Pinales, divided gymnosperms into four classes;
In a later revision, in collaboration with two other taxonomists (1966), Cronquist merged all the gymnosperms into a single division, Pinophyta, with three subdivisions reflecting the main lineages;
In the era of molecular phylogenetics, De-Zhi and colleagues (2004) once again proposed a division of 12 gymnosperm families into two classes;
With the development of the Angiosperm Phylogeny Group came a major realignment of the linear classification of the land plants, by Mark Chase and Reveal (2009). In this system, the land plants form a class, Equisetopsida s.l. ( sensu lato) or sensu Mark Chase & Reveal, also known as embryophytes or Embryophyceae nom. illeg.. Class Equisetopsida s.l. is divided into 14 subclades as subclasses, including Magnoliidae (angiosperms). The gymnosperms are represented by four of these subclasses, placing them in a sister group relationship to angiosperms. Subclasses (number of orders);
There are about 1000 extant gymnosperm species, distributed over about 12 families and 83 genera. Many of these genera are monotypic (41%), and another 27% are oligotypic (2–5 species). The four subclasses have also been treated as divisions of the Spermatophytes. Alternative names and the approximate number of genera and species in each are;
The term Pinophyta has also been used to include all conifers, extinct and extant, with Pinales representing all the extant conifers.
Christenhusz and colleagues extended the system of Chase and Reveal to provide a revised classification of gymnosperms in 2011, based on the above four subclades. In this scheme, the Pinidae comprise three orders, including Pinales, and 6 families;
However, the exact phylogeny remained a topic that was 'hotly debated", in particular whether the main lineages were best represented by the four subclasses of Christenhusz and colleagues or the more traditional five clades (cycads, ginkgos, cupressophytes, Pinaceae and gnetophytes). In 2014 the first complete molecular phylogeny was published, based on 90 species representing all extant genera. This established cycads as the basal group, followed by Ginkgoaceae, as sister to the remaining gymnosperms, and supporting the 'gnepine' hypothesis. This analysis favours the five clade hypothesis, the remaining clade following divergence of the Pinidae, are referred to as the conifer II clade, or cupressophytes, in distinction from the conifer I clade (Gnetidae, Pinidae). This clade, in turn, has two lineages. The first consisting of Sciadopityaceae and the Araucariales, the second being the Cupressales. In the Christenhusz scheme, the Sciadopityaceae were considered to be within Cupressales. The term Cupressaceae s.l. refers to the inclusion of Taxodiaceae. These relationships are shown in this cladogram, although no formal taxonomic revision was undertaken.
A more comprehensive analysis was undertaken by Ran and colleagues in 2018, as part of a detailed phylogeny of all seed plants. This forms the basis of the Tracheophyte Phylogeny Poster and the Angiosperm Phylogeny Website.
Subsequent revisions merged the Taxodiaceae and Cupressaceae, and placed Sciadopitys, formerly in Cupressaceae, into a separate family (Sciadopityaceae). Cephalotaxaceae had previously been recognized as a separate family, but was subsequently included in Taxaceae. Similarly Phyllocladaceae were included in Podocarpaceae. Yews (Taxaceae) have sometimes been treated as a separate order (Taxales).
Christenhusz and colleagues (2011) included only one family in Pinales, Pinaceae, a practice subsequently followed by the Angiosperm Phylogeny Website and the Gymnosperm Database. In this restricted model Pinales (Pinaceae) comprisea 11 genera and about 225 species, all of the other conifers originally included in this order, being included in other orders such as Cupressales.
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