Polystichum


Polystichum is a genus of ferns in the family Dryopteridaceae, subfamily Dryopteridoideae, according to the Pteridophyte Phylogeny Group classification of 2016. The genus has about 500 species and has a cosmopolitan distribution. The highest diversity is in eastern Asia, with about 208 species in China alone; the region from Mexico to Brazil has at least 100 additional species; Africa, North America, and Europe have much lower diversity. Polystichum species are terrestrial or rock-dwelling ferns of warm-temperate and montane-tropical regions. They often are found in disturbed habitat such as road cuts, talus slopes, and stream banks.

Description

Many ferns of this genus have stout, slowly creeping rootstocks that form a crown, with a vase-like ring of evergreen fronds long. The sori are round, with a circular indusium, except in South American species which lack an indusium. The stipes have prominent scales with often have hair-like cilia, but lack any true hairs. The genus differs from the well-known and allied fern genus Dryopteris in the indusium being circular, not reniform, and in having the leaf segments with auricles—asymmetrical blades where one side of the segment is much longer than the other at the base.

Apomixis

, the development of an embryo without the occurrence of fertilization, is particularly common among ferns. Apomixis evolved several times independently in three different clades of polystichoid ferns.

Taxonomy

Polystichum is one of the 10 largest fern genera and is grouped within the Dryopteridaceae. Polystichum s.l. is well defined as its own monophyletic group, including species from the genera Cyrtomidictyum, Cyrtogonellum, Cyrtomium, and Phanerophlebia. Research concerning taxonomy within Polystichum s.s. is ongoing, with high levels of hybridization, allopolyploidy, and apomixis making distinctions difficult. Based on genetic analysis Little & Barrington originally defined a monophyletic Polystichum s.s. by removing Cyrtomium as its own genus. It was further separated by Li et al. into a separate clade along with Phanerophlebia.

Selected species

The genus has a large number of species. The PPG I classification suggested that there were about 500 species; as of 2020, the Checklist of Ferns and Lycophytes of the World listed 397 species and 58 hybrids, noting that "many undescribed species remain". The genus Polystichum includes, but is not limited to, the following species. In this list, a species name preceded by is considered to be a synonym of the accepted species name above it.

*

  • – Aleutian shield fern
  • – Anderson's hollyfern
  • Polystichum atkinsonii
  • Polystichum australiense
  • Polystichum bakerianum
  • Polystichum biaristatum
  • Polystichum bomiense
  • Polystichum bonapartii
  • Polystichum bonseyi – Bonsey's Hollyfern
  • Polystichum brachypterum – Rusty swordfern
  • Polystichum braunii – Braun's shield fern, Braun's hollyfern
  • Polystichum brachypterum
Polystichum garhwalicum
Polystichum michelii
Polystichum minusculum
Polystichum molliculum
  • Polystichum castaneum
  • Polystichum chilense
  • Polystichum christii
  • Polystichum chunii
  • Polystichum craspedosorum
  • Polystichum cyclolobum
  • Polystichum cystostegia – Alpine shield fern
  • Polystichum deltodon
  • Polystichum dielsii
  • Polystichum discretum
  • Polystichum drepanum
  • Polystichum dudleyi – Dudley's sword fern
  • Polystichum duthiei
Polystichum tsuchuense
  • Polystichum echinatum – Rusty swordfern
  • Polystichum erosum
  • Polystichum excellens
  • Polystichum eximium
Polystichum tialooshanense
  • Polystichum falcatipinnum
  • Polystichum falcinellum
  • Polystichum fallax
  • Polystichum formosanum
  • Polystichum glandulosum
  • Polystichum gongboense
Polystichum rarum
  • Polystichum grandifrons
Polystichum kiusiuense
  • Polystichum gymnocarpium
  • Polystichum haleakalense – Island swordfern
  • Polystichum hancockii
  • Polystichum hecatopteron
  • Polystichum herbaceum
  • Polystichum imbricans – Narrowleaf sword fern
  • Polystichum incongruum
  • Polystichum kruckebergii – Kruckeberg's sword fern/holly fern
  • Polystichum kwakiutlii
  • Polystichum lachenense
  • Polystichum lanceolatum
  • Polystichum lemmonii – Lemmon's holly fern, Shasta fern
  • Polystichum lentum
  • Polystichum lonchitis – Holly fern
  • Polystichum longidens
  • Polystichum longipaleatum
  • Polystichum longipes
  • Polystichum luctuosum – Mourning shield fern
  • Polystichum macleae
  • Polystichum macrochlaenum
  • Polystichum makinoi
  • Polystichum martini
  • Polystichum mayebarae
  • Polystichum mediocre
  • Polystichum medogense
  • Polystichum microchlamys
  • Polystichum mohrioides
  • Polystichum mollissimum
  • Polystichum monticola – Mountain shield fern
  • Polystichum moorei
  • Polystichum morii
  • Polystichum moupinense
Polystichum woodsioides
Polystichum solitarium
  • Polystichum muricatum
Polystichum moritzianum
  • Polystichum nakenense
  • Polystichum neolobatum
Polystichum assurgens
Polystichum yigongense
  • Polystichum nepalense
Polystichum atroviridissimum
  • Polystichum ningshenense
  • Polystichum obliquum
  • Polystichum omeiense
Polystichum carvifolium
  • Polystichum ordinatum
Polystichum bicolor
  • Polystichum orientalitibeticum
  • Polystichum paramoupinense
  • Polystichum parvipinnulum
  • Polystichum piceopaleaceum
  • Polystichum polyblepharum – Tassel fern
Polystichum aculeatum var. japonicum
Polystichum setosum
  • Polystichum prescottianum
Polystichum erinaceum
  • Polystichum prionolepis
Polystichum rectipinnum
Polystichum brunneum
  • Polystichum pseudomakinoi
  • Polystichum punctiferum
Polystichum glingense
Polystichum virescens
  • Polystichum pungens – Forest shield fern
Polystichum lucidum
  • Polystichum qamdoense
Polystichum tumbatzense
  • Polystichum retrosopaleaceum
Polystichum aculeatum var. retrosopaleaceum
  • Polystichum rhombiforme
  • Polystichum rhomboidea
Polystichum rhomboideum
  • Polystichum richardii – Common shield fern
  • Polystichum rigens
Polystichum platychlamys
Polystichum mohrioides var. scopulinum
  • Polystichum semifertile
Polystichum nyalamense
Polystichum angulare
  • Polystichum setigerum – Alaska hollyfern
  • Polystichum shensiense
Polystichum lichiangense
  • Polystichum silvaticum
  • Polystichum simplicipinnum
  • Polystichum sinense
Polystichum atuntzeense
Polystichum austrotibeticum
Polystichum decorum
Polystichum ellipticum
Polystichum fukuyamae
Polystichum lhasaense
Polystichum parasinense
Polystichum wilsoni
  • Polystichum squarrosum
Polystichum apicisterile
Polystichum integripinnulum
  • Polystichum stenophyllum
var. conaense Polystichum conaense
  • Polystichum stimulans
Polystichum ilicifolium
  • Polystichum submite
Polystichum paradoxum
  • Polystichum tacticopterum
Polystichum heteropaleaceum
Polystichum kodamae
  • Polystichum thomsoni
  • Polystichum tibeticum
  • Polystichum transvaalense – Stemmed shield fern
  • Polystichum tripteron
  • Polystichum tsus-simense – Korean rock fern
Polystichum falcilobum
  • Polystichum vestitum – Prickly shield fern
  • Polystichum wattii
  • Polystichum whiteleggei
  • Polystichum xiphophyllum
Polystichum monotis
Polystichum praelongum
  • Polystichum yadongense
  • Polystichum yunnanense
Polystichum gyirongense
Polystichum jizhushanense
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Hybrids

is frequent in the genus, with several named hybrids, including:-
Species that were at one time considered part of the genus Polystichum, but are now categorized elsewhere, include:
With species in six continents and many islands, Polystichum is remarkable for its global spread. Polystichum ferns first emerged in Asia during the late Eocene, around 49 million years ago. During this period there were high temperatures across the globe, which may have contributed to the diversification of flora.
Polystichum's spread to the New World took place during the late Eocene to early Oligocene. The most likely dispersal method was across a paratropical forest on a Pacific Ocean land bridge, such as the Bering Land Bridge. For a period before the height of the Ice Age temperatures froze enough seawater to lower the sea level but still allowed a forest to grow in Northern latitudes. From there Polystichum was able to spread through North American and into Central America.
Original theories described Polystichum spreading further into South America from Central America, but recent research has shown that South American Polystichum instead spread through long distance dispersal from Australia. Genetic study has revealed close evolutionary relationships between Polystichum species in these two areas. Both Austral and Austral South American species lack and indusium. Austral Polystichum lack cilia, while South American species have marginal cilia.
Hawaiian Polystichum also spread through long distance dispersal, with two separate dispersal events leading to the three Polystichum now observed in Hawaii.

Ecology

Polystichum species are used as food plants by the larvae of some Lepidoptera species including Pharmacis fusconebulosa. Specimens of some of these can be found at the Royal Botanic Gardens, Sydney.

Cultivation

Several species are grown as ornamental plants in gardens, notably P. setiferum. One species, P. tsus-simense of eastern Asia, is commonly offered as a houseplant.