Pteridophyte Phylogeny Group

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The Pteridophyte Phylogeny Group (PPG) is an informal international group of systematic botanists who collaborate to establish on the classification of pteridophytes (lycophytes and ferns) that reflects knowledge about plant relationships discovered through phylogenetic studies. In 2016, the group published a classification for extant pteridophytes, termed "PPG I". The paper had 94 authors (26 principal and 68 additional). [1] The classification was presented as a consensus classification supported by the community of fern taxonomists, but it has been partially exclusive and is highly contested. Alternative classifications of ferns exist and are preferred by more general taxonomists (see below).

Contents

PPG I

A first classification, PPG I, was produced in 2016, covering only extant (living) pteridophytes. The classification was rank-based, using the ranks of class, subclass, order, suborder, family, subfamily and genus. [1]

Phylogeny

The classification was based on a consensus phylogeny, shown below to the level of order. [1]

tracheophytes

The very large order Polypodiales was divided into two suborders, as well as families not placed in a suborder: [1]

Classification to subfamily level

To the level of subfamily, the PPG I classification is as follows. [1]

  • Order Lycopodiales DC. ex Bercht. & J.Presl (1 family, 16 genera)
  • Subclass Equisetidae Warm. (1 order, 1 family, 1 genus)
  • Order Equisetales DC. ex Bercht. & J.Presl (1 family, 1 genus)
  • Subclass Marattiidae Klinge (1 order, 1 family, 6 genera)
  • Subclass Polypodiidae Cronquist, Takht. & W.Zimm. (7 orders, 44 families, 300 genera)
  • Order Cyatheales A.B.Frank (8 families, 13 genera)
  • Suborder Lindsaeineae Lehtonen & Tuomist (3 families, 9 genera)
  • Suborder Pteridineae J.Prado & Schuettp (1 family, 53 genera)
  • Suborder Aspleniineae H.Schneid. & C.J.Rothf (11 families, 72 genera)

Number of genera

The number of genera used in PPG I has proved controversial. PPG I uses 18 lycopod and 319 fern genera. [1] The earlier system put forward by Smith et al. (2006) had suggested a range of 274 to 312 genera for ferns alone. [2] By contrast, the system of Christenhusz and Chase (2014) used 5 lycopod and about 212 fern genera. [3] The number of fern genera was further reduced to 207 in a subsequent publication. [4]

The number of genera used in each of these two approaches has been defended by their proponents. Defending PPG I, Schuettpelz et al. (2018) argue that the larger number of genera is a result of "the gradual accumulation of new collections and new data" and hence "a greater appreciation of fern diversity and [..] an improved ability to distinguish taxa". They also argue that the number of species per genus in the PPG I system is already higher than in other groups of organisms (about 33 species per genus for ferns as opposed to about 22 species per genus for angiosperms) and that reducing the number of genera as Christenhusz and Chase propose yields the 'excessive' number of about 50 species per genus for ferns. [5] In response, Christenhusz and Chase (2018) argue that the excessive splitting of genera destabilises the usage of names and will lead to greater instability in future, especially when nuclear DNA is employed, and that the highly split genera have few if any characters that can be used to recognize them, making identification difficult, even to generic level. They further argue that comparing numbers of species per genus in different groups is "fundamentally meaningless", because there is no limit to numbers of species per genus. They also argue that the new findings in phylogeny can easily be treated at subgeneric and subfamilial levels, so that the names used by non-specialists will remain unaltered [4] .

See also

Related Research Articles

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Thelypteridaceae is a family of about 900 species of ferns in the order Polypodiales. In the Pteridophyte Phylogeny Group classification of 2016, it is placed in the suborder Aspleniineae. Alternatively, the family may be submerged in a very broadly defined family Aspleniaceae as the subfamily Thelypteridoideae.

<span class="mw-page-title-main">Ophioglossaceae</span> Family of ferns

Ophioglossaceae, the adder's-tongue family, is a small family of ferns. In the Pteridophyte Phylogeny Group classification of 2016, it is the only family in the order Ophioglossales, which together with the Psilotales is placed in the subclass Ophioglossidae. The Ophioglossidae are one of the groups traditionally known as eusporangiate ferns. Members of the family differ from other ferns in a number of ways. Many have only a single fleshy leaf at a time. Their gametophytes are subterranean and rely on fungi for energy.

<span class="mw-page-title-main">Dryopteridaceae</span> Family of ferns

The Dryopteridaceae are a family of leptosporangiate ferns in the order Polypodiales. They are known colloquially as the wood ferns. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), the family is placed in the suborder Polypodiineae. Alternatively, it may be treated as the subfamily Dryopteridoideae of a very broadly defined family Polypodiaceae sensu lato.

<span class="mw-page-title-main">Pteridophyte</span> Group of plants that reproduce by spores

A pteridophyte is a vascular plant that reproduces by means of spores. Because pteridophytes produce neither flowers nor seeds, they are sometimes referred to as "cryptogams", meaning that their means of reproduction is hidden.

<span class="mw-page-title-main">Polypodiaceae</span> Family of ferns

Polypodiaceae is a family of ferns. In the Pteridophyte Phylogeny Group classification of 2016, the family includes around 65 genera and an estimated 1,650 species and is placed in the order Polypodiales, suborder Polypodiineae. A broader circumscription has also been used, in which the family includes other families kept separate in PPG I. Nearly all species are epiphytes, but some are terrestrial.

<span class="mw-page-title-main">Blechnaceae</span> Family of ferns

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<span class="mw-page-title-main">Pteridaceae</span> Family of ferns

Pteridaceae is a family of ferns in the order Polypodiales, including some 1150 known species in ca 45 genera, divided over five subfamilies. The family includes four groups of genera that are sometimes recognized as separate families: the adiantoid, cheilanthoid, pteridoid, and hemionitidoid ferns. Relationships among these groups remain unclear, and although some recent genetic analyses of the Pteridales suggest that neither the family Pteridaceae nor the major groups within it are all monophyletic, as yet these analyses are insufficiently comprehensive and robust to provide good support for a revision of the order at the family level.

<span class="mw-page-title-main">Athyriaceae</span> Family of ferns

The Athyriaceae are a family of terrestrial ferns in the order Polypodiales. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), the family is placed in the suborder Aspleniineae, and includes two genera. Alternatively, it may be treated as the subfamily Athyrioideae of a very broadly defined family Aspleniaceae. The family has with a cosmopolitan distribution.

<i>Aleuritopteris</i> Genus of ferns

Aleuritopteris is a genus of ferns in the Cheilanthoideae subfamily of the Pteridaceae. As with some other genera of the Cheilanthoideae, molecular phylogenetic studies have suggested that it is not monophyletic, and so may need to be circumscribed differently in future.

<i>Campyloneurum</i> Genus of ferns

Campyloneurum is a genus of ferns in the family Polypodiaceae, subfamily Polypodioideae, according to the Pteridophyte Phylogeny Group classification of 2016 (PPG I). They are commonly known as strap ferns.

<span class="mw-page-title-main">Lindsaeaceae</span> Family of ferns

Lindsaeaceae is a pantropical family of ferns in the order Polypodiales. It contains six or seven genera with about 220 known species, some of which also extend into the more temperate regions of eastern Asia, New Zealand, and South America.

<span class="mw-page-title-main">Cystopteridaceae</span> Family of ferns

Cystopteridaceae is a family of ferns in the order Polypodiales. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), the family is placed in the suborder Aspleniineae of the order Polypodiales, and includes three genera. Alternatively, it may be treated as the subfamily Cystopteridoideae of a very broadly defined family Aspleniaceae.

<span class="mw-page-title-main">Tectariaceae</span> Family of ferns

Tectariaceae is a family of leptosporangiate ferns in the order Polypodiales. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), the family is placed in the suborder Polypodiineae. Alternatively, it may be treated as the subfamily Tectarioideae of a very broadly defined family Polypodiaceae sensu lato. The family comprises seven genera, of which Tectaria is by far the largest.

<span class="mw-page-title-main">Microsoroideae</span> Subfamily of ferns

Microsoroideae is a subfamily in the fern family Polypodiaceae in the Pteridophyte Phylogeny Group classification of 2016 (PPG I). The subfamily is also treated as the tribe Microsoreae within a very broadly defined family Polypodiaceae sensu lato. In either treatment, it includes the previously separated tribe Lepisoreae.

<span class="mw-page-title-main">Polypodioideae</span> Subfamily of ferns

Polypodioideae is a subfamily belonging to the fern family Polypodiaceae, which is a member of the suborder Polypodiineae in the Pteridophyte Phylogeny Group classification of 2016 (PPG I). Alternatively, the subfamily may be treated as the tribe Polypodieae within a very broadly defined family Polypodiaceae sensu lato.

<span class="mw-page-title-main">Diplaziopsidaceae</span> Family of ferns

Diplaziopsidaceae is a family of ferns in the order Polypodiales. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), the family is placed in the suborder Aspleniineae, and includes two genera. Alternatively, it may be treated as the subfamily Diplaziopsidoideae of a very broadly defined family Aspleniaceae.

Loxogrammoideae is a small subfamily of the fern family Polypodiaceae in the Pteridophyte Phylogeny Group classification of 2016 (PPG I), with two genera, Dictymia and Loxogramme. The subfamily was previously considered to be a separate family, LoxogrammaceaeChing ex Pic.Serm., and is also treated as the tribe Loxogrammeae within a very broadly defined family Polypodiaceae sensu lato. Molecular phylogenetic studies place the group within Polypodiaceae.

<span class="mw-page-title-main">Lindsaeineae</span> Suborder of ferns

Lindsaeineae is a suborder of ferns (Polypodiopsida), order Polypodiales, created by the Pteridophyte Phylogeny Group (2016). It consists of two monogeneric families plus the larger Lindsaeaceae with seven genera, and the suborder contains about 237 species overall. It corresponds to Lindsaeaceae sensu Smith 2016.

<i>Parablechnum</i> Genus of ferns

Parablechnum is a genus of ferns in the family Blechnaceae, subfamily Blechnoideae, according to the Pteridophyte Phylogeny Group classification of 2016. The genus is accepted in a 2016 classification of the family Blechnaceae, but other sources sink it into a very broadly defined Blechnum, equivalent to the whole of the PPG I subfamily.

References

  1. 1 2 3 4 5 6 PPG I (2016), "A community-derived classification for extant lycophytes and ferns", Journal of Systematics and Evolution, 54 (6): 563–603, doi: 10.1111/jse.12229
  2. ↑ Smith, Alan R.; Pryer, Kathleen M.; Schuettpelz, Eric; Korall, Petra; Schneider, Harald & Wolf, Paul G. (2006), "A Classification for Extant Ferns", Taxon, 55 (3): 705–731, doi:10.2307/25065646, JSTOR   25065646
  3. ↑ Christenhusz, Maarten J. M. & Chase, Mark W. (2014), "Trends and concepts in fern classification", Annals of Botany, 113 (4): 571–594, doi: 10.1093/aob/mct299 , PMC   3936591 , PMID   24532607
  4. 1 2 Christenhusz, Maarten J. M. & Chase, Mark W. (2018), "PPG recognises too many fern genera", Taxon, 67 (3): 481–487, doi: 10.12705/673.2
  5. ↑ Schuettpelz, Eric; Rouhan, Germinal; Pryer, Kathleen M.; Rothfels, Carl J.; Prado, Jefferson; Sundue, Michael A.; Windham, Michael D.; Moran, Robbin C. & Smith, Alan R. (2018), "Are there too many fern genera?", Taxon, 67 (3): 473–480, doi: 10.12705/673.1
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