Pteridophyte Phylogeny Group

The Pteridophyte Phylogeny Group (PPG) is an informal international group of systematic botanists who collaborate to establish a consensus 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]

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]

Polypodiales
Saccolomatineae

Saccolomataceae

Lindsaeineae

Dennstaedtiineae

Dennstaedtiaceae

eupolypods

Suborder Aspleniineae (eupolypods II)

Suborder Polypodiineae (eupolypods I)

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)
  • Subfamily Lycopodielloideae W.H.Wagner & Beitel ex B.Øllg. (4 genera)
  • Subfamily Lycopodioideae W.H.Wagner & Beitel ex B. Øllg. (9 genera)
  • Subfamily Huperzioideae W.H.Wagner & Beitel ex B. Øllg. (3 genera)
  • Family Isoëtaceae Dumort. (1 genus)
  • Class Polypodiopsida Cronquist, Takht. & W.Zimm. (11 orders, 48 families, 319 genera)
  • Subclass Equisetidae Warm. (1 order, 1 family, 1 genus)
  • Order Equisetales DC. ex Bercht. & J.Presl (1 family, 1 genus)
  • Subclass Ophioglossidae Klinge (2 orders, 2 families, 12 genera)
  • Subfamily Helminthostachyoideae C.Presl (1 genus)
  • Subfamily Mankyuoideae J.R.Grant & B.Dauphin (1 genus)
  • Subfamily Ophioglossoideae C.Presl (4 genera)
  • Subfamily Botrychioideae C.Presl (4 genera)
  • Subclass Marattiidae Klinge (1 order, 1 family, 6 genera)
  • Subclass Polypodiidae Cronquist, Takht. & W.Zimm. (7 orders, 44 families, 300 genera)
  • Subfamily Trichomanoideae C.Presl (8 genera)
  • Subfamily Hymenophylloideae Burnett (1 genus)
  • Order Gleicheniales Schimp (3 families, 10 genera)
  • Family Matoniaceae C.Pres (2 genera)
  • Family Dipteridaceae Seward & E.Dale (2 genera)
  • Family Gleicheniaceae C.Presl (6 genera)
  • Order Schizaeales Schimp. (3 families, 4 genera)
  • Order Cyatheales A.B.Frank (8 families, 13 genera)
  • Family Thyrsopteridaceae C.Presl (1 genus)
  • Family Loxsomataceae C.Presl (2 genera)
  • Family Culcitaceae Pic.Serm (1 genus)
  • Family Plagiogyriaceae Bowe (1 genus)
  • Family Cibotiaceae Koral (1 genus)
  • Family Metaxyaceae Pic.Serm. (1 genus)
  • Family Dicksoniaceae M.R.Schomb. (3 genera)
  • Family Cyatheaceae Kaulf. (3 genera)
  • Suborder Saccolomatineae Hovenkamp (1 family, 1 genus)
  • Family Saccolomataceae Doweld (1 genus)
  • Suborder Lindsaeineae Lehtonen & Tuomist (3 families, 9 genera)
  • Family Cystodiaceae J.R.Croft (1 genus)
  • Family Lonchitidaceae Doweld (1 genus)
  • Family Lindsaeaceae C.Presl ex M.R.Schomb. (7 genera)
  • Suborder Pteridineae J.Prado & Schuettp (1 family, 53 genera)
  • Subfamily Parkerioideae Burnett (2 genera)
  • Subfamily Cryptogrammoideae S.Lindsay (3 genera)
  • Subfamily Pteridoideae Link (13 genera)
  • Subfamily Vittarioideae Link (12 genera)
  • Subfamily Cheilanthoideae Horvat (23 genera)
  • Suborder Aspleniineae H.Schneid. & C.J.Rothf (11 families, 72 genera)
  • Family Cystopteridaceae Shmakov (3 genera)
  • Family Rhachidosoraceae X.C.Zhang (1 genus)
  • Family Diplaziopsidaceae X.C.Zhang & Christenh. (2 genera)
  • Family Desmophlebiaceae Mynssen (1 genus)
  • Family Hemidictyaceae Christenh. & H.Schneid. (1 genus)
  • Family Aspleniaceae Newman (2 genera)
  • Family Woodsiaceae Herter (1 genus)
  • Family Onocleaceae Pic.Serm. (4 genera)
  • Family Blechnaceae Newman (24 genera)
  • Family Athyriaceae Alston (3 genera)
  • Family Thelypteridaceae Ching ex Pic.Serm. (30 genera)
  • Suborder Polypodiineae Dumort. (9 families, 108 genera)
  • Family Didymochlaenaceae Ching ex Li Bing Zhang & Liang Zhang (1 genus)
  • Family Hypodematiaceae Ching (2 genera)
  • Family Dryopteridaceae Herter (26 genera)
  • Subfamily Polybotryoideae H.M.Liu & X.C.Zhang (7 genera)
  • Subfamily Elaphoglossoideae (Pic.Serm.) Crabbe, Jermy & Mickel (11 genera)
  • Subfamily Dryopteridoideae Link (6 genera)
  • 2 genera not assigned to a subfamily
  • Family Nephrolepidaceae Pic.Serm. (1 genus)
  • Family Lomariopsidaceae Alston (4 genera)
  • Family Tectariaceae Panigrahi (7 genera)
  • Family Oleandraceae Ching ex Pic.Serm. (1 genus)
  • Family Davalliaceae M.R.Schomb. (1 genus)
  • Family Polypodiaceae J.Presl & C.Presl (65 genera)
  • Subfamily Loxogrammoideae H.Schneid. (2 genera)
  • Subfamily Platycerioideae B.K.Nayar (2 genera)
  • Subfamily Drynarioideae Crabbe, Jermy & Mickel (6 genera)
  • Subfamily Microsoroideae B.K.Nayar (12 genera)
  • Subfamily Polypodioideae Sweet (9 genera)
  • Subfamily Grammitidoideae Parris & Sundue (33 genera)
  • 1 genus not assigned to a subfamily

Number of genera

The number of genera used in PPG I has proved controversial. PPG I uses 18 lycophyte 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 lycophyte 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, 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".[4]

See also
  • List of fern families

References
  1. 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. 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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