Polystichum

Polystichum is a genus of ferns in the family Dryopteridaceae, subfamily Dryopteridoideae, according to the Pteridophyte Phylogeny Group classification of 2016 (PPG I). 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 (at least 17 species), North America (at least 18 species), and Europe (at least 5 species) have much lower diversity. Polystichum species are terrestrial or rock-dwelling ferns of warm-temperate and montane-tropical regions (a few species grow in alpine regions). They are often found in disturbed habitats 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
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 (2003) originally defined a monophyletic Polystichum s.s. by removing Cyrtomium as its own genus. It was further separated by Li et al. (2008) 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; , 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.
– Christmas fern
– Hard shield fern
(=)
– 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 bulbiferum
Polystichum calderonense – Monte Guilarte hollyfern
Polystichum californicum – California sword fern
Polystichum capillipes (=) 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 munitum – Western sword fern(=) 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 proliferum – Mother shield fern
Polystichum pseudocastaneum (=) 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 rotundilobum
Polystichum scopulinum – Mountain holly fern, rock sword fern(=) Polystichum mohrioides var. scopulinum
Polystichum semifertile (=) Polystichum nyalamense
Polystichum setiferum – Soft shield fern(=) 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
Hybrids
Hybridisation is frequent in the genus, with several named hybrids, including:-
P. × bicknellii (P. aculeatum × P. setiferum)
P. × illyricum (P. aculeatum × P. lonchitis)
P. × lonchitiforme (P. lonchitis × P. setiferum)
P. × lesliei (P. setiferum × P. munitum) first found in Surrey in 1995 and a second plant found in Cornwall in 2001.
Former species
Species that were at one time considered part of the genus Polystichum, but are now categorized elsewhere, include:
Polystichum auriculatum = Dryopteris auriculata
Polystichum falcatum = Cyrtomium falcatum – Japanese Holly Fern
Polystichum lepidocaulon = Cyrtomidictyum lepidocaulon
Distribution
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.
References
External links
Jepson Manual Treatment
the Polystichum homepage
Dryopteridaceae
Fern genera
Garden plants