Pteridophyte Phylogeny Group

Source: Wikipedia, the free encyclopedia.

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
Lycopodiopsida

Lycopodiales

Isoëtales

Selaginellales

euphyllophytes
Polypodiopsida
Ophioglossidae

Psilotales

Ophioglossales

Marattiidae

Marattiales

Polypodiidae

spermatophytes

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

Polypodiales
Saccolomatineae

Saccolomataceae

Lindsaeineae

Pteridineae

Pteridaceae

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)
  • Order
    Isoëtales
    Prantl (1 family, 1 genus)
  • Family
    Isoëtaceae
    Dumort. (1 genus)
  • Order
    Selaginellales
    Prantl (1 family, 1 genus)
  • Family
    Selaginellaceae
    Willk (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)
  • Order
    Psilotales
    Prant (1 family, 2 genera)
  • Order
    Ophioglossales
    Link (1 family, 10 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)
  • Order
    Marattiales
    Link (1 family, 6 genera)
  • Subclass
    Polypodiidae
    Cronquist, Takht. & W.Zimm. (7 orders, 44 families, 300 genera)
  • Order
    Osmundales
    Link (1 family, 6 genera)
  • Order
    Hymenophyllales
    A.B.Frank (1 family, 9 genera)
  • Subfamily
    Trichomanoideae
    C.Presl (8 genera)
  • Subfamily
    Hymenophylloideae
    Burnett (1 genus)
  • Family
    Lygodiaceae
    M.Roem (1 genus)
  • Family Schizaeaceae Kaulf (2 genera)
  • Family
    Anemiaceae
    Link (1 genus)
  • 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)
  • 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)
  • Suborder
    Dennstaedtiineae
    Schwartsb. & Hovenkamp (1 family, 10 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)
  • Subfamily
    Stenochlaenoideae
    (Ching) J.P.Roux (3 genera)
  • Subfamily
    Woodwardioideae
    Gasper (3 genera)
  • Subfamily
    Blechnoideae
    Gasper, V.A.O.Dittrich & Salino (18 genera)
  • Subfamily
    Phegopteridoideae
    Salino, A.R.Sm. & T.E.Almeid (3 genera)
  • Subfamily
    Thelypteridoideae
    C.F.Reed (27 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)

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

References