Saturday, June 11, 2011
Dryopteris guanchica, an allotetraploid hybrid fern of Miocene
The Miocene was the cradle of a large number of existing plants, many of them the result of interspecific hybridization and subsequent successful adaptive mutations that allowed them to survive the sudden changes of that tumultuous period. One of these plants is the fern Dryopteris guanchica, an allotetraploid hybrid fruit cross between Dryopteris aemula and Dryopteris maderensis. Belongs to the family of Aspidiaceae. Its chromosome number is 2n = 164, n = 82.
Magnificent specimen of Dryopteris guanchica in early May in the path of Vueltas de Taganana in Anaga Massif located in the far north of the island of Tenerife. The fern was old fronds and new fronds, having just sprouting spring issue. The Dryopteris guanchica, like most ferns arose during the Miocene, it grows in the Macaronesian region and the Iberian Peninsula (humid forests of Northern Spain, Galicia, Sierra de Sintra and Sierras de Algeciras), in one day was a vast region covered with forests of laurel. About 6 million years ago, during a very cold and dry period in that the water of Atlantic Ocean descended about 100 meters below the current level (in the Great Messinian salinity crisis that lasted a million years), land shallower European and African coasts and the Macaronesian islands emerged out of the sea and, having little water to separate them, facilitated the exchange of plant and animal species and interspecific hybridization between related plants. This allows us to understand why the genes of an endemic fern to Madeira, the Dryopteris maderensis, found on a fern Dryopteris guanchica as in regions as distant from Madeira. Dryopteris guanchica curiously does not grow in this beautiful Portuguese island, where live nevertheless both diploid parents, Dryopteris aemula and Dryopteris maderensis.
Another issue of Dryopteris guanchica on the same path of Taganana Turns. We will see the new fronds sprouting vigorously. The photos are very bright due to camera flash, as really living in a twilight intense in the understory of a thick, almost impenetrable rain forest of laurel. Dryopteris guanchica is one of the most demanding habitat type of Aspidiaceae, then it need to live in a very dark habitat on a acid substrate permanently wet. Other Aspidiaceae of Anaga Massif as Dryopteris oligodonta and Polystichum setiferum are less demanding environments and can tolerate more light and less humid.
Dryopteris guanchica in the forest track along the trail of Pijaral that goes from Roque Anambra to the viewpoint of Cabezo del Tejo. In the Canary Islands, besides Dryopteris guanchica, grows also its ancestor Dryopteris aemula, as well as Dryopteris affinis and Dryopteris oligodonta. Some botanists say they have found also Dryopteris maderensis in the Canaries, but in any case would be very few copies. Its existence outside of Madeira could be explained by recent colonization by spores carried by wind or stuck in the feathers and feet of sea birds or an old land-land settlement during the Messinian period in that the Canary archipelago and maderense archipelago sometime came to form a continuum without water than separated.
Wide triangular-lanceolate frond of Dryopteris guanchica an intense dark green color, soft touch and consistency pinnae very crisp tender. Can reach 115 cm in length. Its petiole yellowish-brown with abundant brown lanceolate paleae in their basal part is longer than the blade.
The frond of Dryopteris guanchica consists of asymmetrical pinnae especially the pair of basal pinnae frond (seen in the photo below), as acroscopic pinnules are less developed than basiscopic. Both the rachis of the frond and rachis of the pinnae and the pinnules are grooved on its upper surface along its entire length.
The pinnae are divided three to four times in petiolulate pinnules, triangular-lanceolate, with serrated edge and corner teeth convergent or directed toward the apex of the pinnules. It looks great channel that runs along the top of the spine.
Immature sori of Dryopteris guanchica in early May. Enlarging the picture double click the details look better.
All Dryopteris sori are reniform (kidney shaped). In the photo of these immature sori we see the white and transparent indusium that covers the sporangia.
Dryopteris guanchica mature sori in early May. These sori matured at the end of last summer and the sporangia have already dispersed spores.
In these mature sori the indusium is looming up leaving the tiny sporangia months ago deployed and dispersed the spores at the optimum time for germination.