Dryopteridaceae

The wood ferns, or Dryopteridaceae, are a family of leptosporangiate ferns within the order Polypodiales. According to the 2016 Pteridophyte Phylogeny Group classification (PPG I), they belong to the suborder Polypodiineae. Alternatively, they can be treated as the subfamily Dryopteridoideae within a broadly defined Polypodiaceae. The family contains roughly 1,700 species and is found worldwide.

These ferns can grow on the ground, on rocks, as hemiepiphytes, or as true epiphytes, and many are grown as ornamentals. The four largest genera—Elaphoglossum (over 600 species), Polystichum (260), Dryopteris (225), and Ctenitis (150)—account for about 70% of all species. The group split from other eupolypods I families around 100 million years ago, and the earliest known fossils date to about 99 million years ago in the Mid Cretaceous.

Description

The rhizomes are often stout and may creep, ascend, stand erect, or sometimes climb; they are covered with nonclathrate scales at the tips. Fronds are usually monomorphic, though sometimes dimorphic, and may be scaly or glandular but rarely hairy. The petioles contain numerous round vascular bundles arranged in a ring (or rarely as few as three), with the adaxial bundles being largest. Veins are pinnate or forking, free or variously joined into areoles that may or may not contain included veinlets.

Sori are typically round, though in a few lineages they are acrostichoid (covering the entire lower leaf surface). They are usually covered by an indusium, which is round-reniform or peltate, but sometimes lack one. Sporangia have three-rowed stalks of varying length, and the spores are kidney-shaped, monolete, and have a perine or wings.

History

Taxonomically, Karl U. Kramer and colleagues defined the Dryopteridaceae broadly in 1990 to include what are now the Woodsiaceae, Onocleaceae, and most Tectariaceae. Molecular studies later showed this version to be polyphyletic, and it was split up by Smith and others in 2006. The inclusion of Didymochlaena, Hypodematium, and Leucostegia is uncertain; if these three are excluded, the family is strongly supported as monophyletic, and some authors have already placed them elsewhere.

In 2007, DNA evidence moved Pleocnemia from Tectariaceae into Dryopteridaceae. In 2010, Arthrobotrya was resurrected from Teratophyllum in a study of bolbitidoid ferns, and later that year Mickelia was described as a new genus. Some species once placed in Oenotrichia have been removed because they do not belong there or in Dennstaedtiaceae; they likely belong in Dryopteridaceae but have not yet been assigned a genus.

A 2012 phylogenetic study of Dryopteris and its relatives merged Acrophorus, Acrorumohra, Diacalpe, Dryopsis, Nothoperanema, and Peranema into that genus. The 2013 Flora of China treatment used phylogenetic results to sink Lithostegia and Phanerophlebiopsis into Arachniodes. Under the 2014 classification of Christenhusz and Chase, Dryopteridaceae was submerged as subfamily Dryopteridoideae within Polypodiaceae, but the PPG I classification of 2016 retained it as a family.

Subdivision

The PPG I system divides the family into three subfamilies: Polybotryoideae (including Cyclodium, Maxonia, Olfersia, Polybotrya, Polystichopsis, Stigmatopteris, and Trichoneuron), Elaphoglossoideae (including Arthrobotrya, Bolbitis, Elaphoglossum, Lastreopsis, Lomagramma, Megalastrum, Mickelia, Parapolystichum, Pleocnemia, Rumohra, and Teratophyllum), and Dryopteridoideae (including Arachniodes, Ctenitis, Cyrtomium, Dryopteris, Phanerophlebia, Polystichum, and Stenolepia). Didymochlaena has been moved to Didymochlaenaceae, and Hypodematium and Leucostegia to Hypodematiaceae. Aenigmopteris, once suggested for this family based on its similarity to Ctenitis, has been placed within Tectaria (Tectariaceae) by molecular phylogeny. Dryopolystichum now belongs to Lomariopsidaceae.