Friday, February 4, 2011

Woodwardia radicans, the giant of laurel forest

Woodwardia radicans is the largest fern of laurel forests. Their fronds can reach 2.5 meters in length, beating the other giant, Culcita macrocarpa. Precisely these two large ferns, along with Selaginella balansae, are considered the oldest settled during the Late Cretaceous in the western Mediterranean region from ancient African and Asian ferns, perhaps over a period of warm subtropical climate. Its current natural distribution seems to support this hypothesis, since it lives in the Macaronesian Islands: Canary Islands, Madeira and Azores (except in the Cape Verde Islands), the Cantabrian-Atlantic coast of the Iberian peninsula: Galicia, Asturias, Cantabria and Basque country, in northern Algeria and also in the south of the Italian peninsula, Sicily, Corsica and Crete. Existing populations in the Serra de Sintra in Portugal are not natural.

Beautiful example of Woodwardia radicans in a clearing of a laurel forest of Madeira Island near Funchal at the beginning of May. (Double click on the photo to enlarge)

Because of its great beauty has been cultivated in many countries around the world, existing feral populations in Asia and North America, for example, in Florida and California. Belongs to the family of Blechnaceae, like the Doodia caudata, the Blechnum brasiliense and Blechnum spicant. Its chromosome number is 2n = 68. The genus Woodwardia was devoted to English botanist Thomas J. Woodward (1745-1820), specialized in cryptogamic plants.

In the Canary Islands it is called Pijara, Penco labrado, Pirgua and Helecho de cumbre, in Portugal and Galicia is called Feto de botâo, in Italia Felce bulbifera and in English Chain fern or Rooting chainfern.

Its scientific name refers to the ability of this fern to reproduce vegetatively from small bulblets, buds and shoots, that as small rhizomes brown paleae covered grow in the apical end of the fronds. When these bulblets come into contact with the ground, take root and begin to grow as independent ferns. Thus botanists gave it the name "radicans" =  that takes roots.

Great Woodwardia radicans fronds hanging on the wall of a ravine of Bosque de los Tiles on the island of La Palma. The older fronds were arching to looking for a contact point on the land of the wall and then the small bulblets that grows at the end of the frond takes root and gives rise to a new identical clonal fern his mother.

Their preferred habitat are the moist and shady ravines and forests, both vertical walls, as in the understory and in deep crevices of rocks. In the Cantabrian coast, when massive forest clearing and the forest is naked without the protective cover from the tops of the trees, Woodwardia are left to frost and die with fronds burned from the cold.

Three young specimens of Woodwardia radicans in the northwest slope of the volcanic mountain called Caldeira do Faial in the island of the same name of the Azores Archipelago. Can see the thick brown rhizome paleae covered.

Impressive frond of two meters long hanging in the Bosque de los Tiles on the Canary island of La Palma. The blade is ovate-lanceolate, sometimes triangular, caudate pinnae more than 30 cms. The pinnules are subfalcate slightly serrulated. (Double click on the photo to enlarge)

Woodwardia radicans new frond displaying their pinnae in early May.

Here you can see the reason for the name "radicans", a bud or bulbil that grow on the tips of the fronds and when it touches the ground it takes root and gives rise to a new fern. In this way it can produce an entire population of Woodwardia radicans genetically identical to the original fern that was born from a spore.

This photo shows bulbils already rooted in the tip of a frond of Woodwardia radicans grown in a garden of Mallorca. These clonic shoots can be left grow around their mother or are cut from the frond and transplanted to another site partially shaded and sheltered from cold winds from the north. In summer, they need regular watering if it not rains. For cutting and transplanting is not necessary to wait to take root. You can also put a flowerpot near the mother holding the bulblets on the ground of the flowerpot and, when it is rooted, already you can cut the tip of the frond.

Same small bulbil after planted. A few weeks begin to sprout new fronds and two years after reaching maturity.

Woodwardia radicans mature sori in January with the indusium sporangia up to be deployed and disperse the spores.

Details of previous sori, which are typical of the family Blechnaceae and are embedded deep into the underside of the pinnae, forming two parallel rows attached to the midrib of each pinna. Double clicking on the photo for a larger look great displayed sporangia, peeking below the convex and leathery indusium.

Microscopic photograph of a sporangium of Woodwardia radicans now empty after the dispersal of spores. Above left is the sporangiophore formed by  tubular cells, which is attached to the pinna and makes the role of umbilical cord, feeding the sporangium which form the spores in the transparent bag.

Dark yellowish spores of Woodwardia radicans with subreticulated perispore, viewed to the microscope at 400 magnification.

1 comment:

  1. Beatiful forest of Woodwardia in the Valle delle Ferriere outside of Amalfi.