Lygodium

Lygodium (climbing fern) is a genus of about 40 species of ferns, native to tropical regions across the world, with a few temperate species in eastern Asia and eastern North America. It is the sole genus in the family Lygodiaceae in the Pteridophyte Phylogeny Group classification of 2016 (PPG I). Alternatively, the genus may be placed as the only genus in the subfamily Lygodioideae of a more broadly defined family Schizaeaceae, the family placement used in Plants of the World Online. Per recent molecular evidence, Lygodiaceae is thought to have diverged relatively early from the other members of the Schizaeales due to the relatively high level of synonymous sequence divergence between the families within the Schizaeales.

Description
Lygodium are unusual in that the rachis, or midrib, of the frond is thin, flexible, and long, the frond unrolling with indeterminate growth and the rachis twining around supports, so that each frond forms a distinct vine. The fronds may be from 3-12 m long, depending on the species. They are also easily identifiable by their possession of apical buds that lay dormant until damage to the rachis occurs, allowing them a high degree of endurance.

Range
Lygodium is a wide ranging genus with native populations existing in Asia, Australasia, Africa, and North and South America. The genus is largely pan-tropical, with the center of diversity being Pacific islands, such as Borneo, the Philippine islands, and New Guinea. There do exist several species tolerant of temperate climates such as Lygodium palmatum, which is endemic to the Appalachian region of eastern North America, and Lygodium japonicum, which is native to Japan, but highly invasive in the Southeastern United States. For more on this, refer to the "As invasive species" section below. The lack of extant Lygodium species in Europe is commonly attributed to the Pleistocene glaciation wiping them out. Similar extirpations did not occur in other high middle and high latitude areas, such as the United States and Japan that do have Lygodium populations at present. This discrepancy is thought to be due to the East-West orientation of the European Alps preventing southward migration of Lygodium members, among other extirpated species, while the relatively North-South orientations of the Appalachian mountains and Japanese Alps allowed such southward migration.

Uses
Lygodium species, known as nito, are used as a source of fibers in the Philippines. The fibers are used as material for weaving, most notably of traditional salakot headgear.

As invasive species
Some Lygodium species are now considered very problematic invasive weeds in the southeastern United States. Populations of Lygodium have increased more than 12-fold over the past decade, as noted by Florida's Institute of Food and Agricultural Sciences.

Japanese climbing fern (Lygodium japonicum) was added to the Florida Noxious Weed List in 1999. It is also a major problem in pine plantations, causing contamination and harvesting problems for the pine straw industry. Old World climbing fern (Lygodium microphyllum) infests cypress swamps and other hydric sites, forming a monoculture. This massive infestation displaces all native flora and fauna, completely changing the ecosystem of the area.

Plants in this genus have basal chromosome counts of n=28, 29, 30.

Selected species

 * Lygodium altum (Clarke) Alderw. 1909
 * Lygodium articulatum A.Rich. 1832 – New Zealand (North Island).
 * Lygodium auriculatum (Willd.) Alston 1959
 * Lygodium boivinii Kuhn 1868
 * Lygodium borneense Alderw. 1915
 * Lygodium circinatum (Burm.fil.) Sw. 1806 – Tropical Asia and Australasia.
 * ?Lygodium conforme – China.
 * Lygodium cubense Kunth 1815 – Cuba, Hispaniola.
 * ?Lygodium digitatum – China.
 * Lygodium dimorphum Copel. 1911
 * Lygodium flexuosum (L.) Sw. 1801 – Southern China south to northern Australasia, Kerala(South India).
 * Lygodium heterodoxum Kunze 1849
 * Lygodium hians E.Fourn. 1873
 * Lygodium japonicum (Thunb.) Sw. 1801 – Japanese climbing fern. Eastern Asia south to northern Australia.
 * Lygodium kerstenii Kuhn 1867
 * Lygodium lanceolatum Desv. 1811
 * Lygodium longifolium (Willd.) Sw. 1803
 * Lygodium merrillii Copel. 1907
 * Lygodium microphyllum (Cav.) R. Br. 1810 – Old World climbing fern. Africa, south Asia and Australia.
 * ?Lygodium microstachyum – China.
 * Lygodium oligostachyum (Willd.) Desv. 1827
 * Lygodium palmatum (Bernh.) Swartz 1806 – American climbing fern. Eastern United States (rare, confined to acid soils).
 * Lygodium polystachyum Wall. ex Moore 1859 – China.
 * Lygodium radiatum Prantl 1881
 * Lygodium reticulatum Schkuhr 1809 – Australia, Polynesia.
 * Lygodium salicifolium Presl 1845 – Southern China south to northern Australasia.
 * ?Lygodium subareolatum – China.
 * Lygodium smithianum Presl 1845
 * Lygodium trifurcatum Baker 1868 – Tropical southeast Asia south to northern Australasia.
 * Lygodium venustum Sw. 1803
 * Lygodium versteeghii Christ 1909 – Tropical southeast Asia south to northern Australasia.
 * Lygodium volubile Sw. 1803 – Northern South America, Central America, Caribbean.
 * Lygodium yunnanense Ching 1959 – Southern China.
 * L. ×fayae Jermy & Walker 1985
 * L. ×lancetillanum Gómez 1980