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