Pteris incompleta: a spectacular fern

It is in extinction danger

I saw it for the first time in a very humid and shady precipice under the dense tops of a forest of laurisilva, located in the North skirt of Monte Carneiro of the small Azorian island of Faial. It was an old gigantic unit with long fronds of black petiole extended towards the little light that filtered between the leaves of the cover forest. The ambient was very humid, smelled of good earth and the ebullient vegetation transported me to last times, when the nature was still a paradise.

 

Magestic Pteris incompleta in Faial Island. Their fronds surpassed the 150 cms. of length. I recommend to extend the photos with a double click.

 Lowering by the footpath of the Vueltas de Taganana in the heat of Rural Park of Anaga located in the North end of Tenerife Island I found this beautiful Pteris incompleta full of life, appearing vigorously new fronds at the beginning of May. 

Pteris incompleta belongs to the Pteridaceae family and lives in all the Macaronesia (Canary, Azores and Madeira, except Cape Verde), in the north of Morocco (Tangiers) and in two localities of the Iberian Peninsula (Natural Park of Los Alcornocales in the Spanish province of Cadiz and Mountain range of Sintra in Portugal near Lisbon). It is a very little fern and is catalogued in danger of extinction in the Red List of the Spanish Vascular Flora.

Near image of the great fronds of previous Pteris incompleta. The apex of the lamina and pinnae are caudate or acuminate, that is to say, is extended and narrow in the form of tail. The lamina has pinnatisect pinnae in the apex, bipinnatisect in the average part and tripinnatisect in the base. Raquis is green. The petiole has a nice jet black color and is shorter than the lamina. 

In this image the black petioles of the fronds are seen well. This young Pteris incompleta was photographed in the Vulcao dos Capelinhos located in the North end of Faial Island in the Azores Archipelago, where the last volcanic eruption in Portuguese territory in 1957 took place.

Linear-lanceolate pinnae obliquely inserted in rachis of the lamina in alternate or subopposite form.

The pinnules are slightly falcate and no petiolulate and obliquely inserted with a large base on rachis of the pinna.

The sori are perhaps the prettiest and identifying part of Pteris incompleta. They are located in the edge of the pinnules, being greater the sorus of the basal margin. Its name "incompleta" it must to that, unlike the majority of Pteridaceae, the sori of Pteris incompleta do not occupy all the edge of the pinnule, but only between 1/5 and 2/3 of the same. Each sorus is covered by entire, scarious and persistent pseudoindusium of a target-grayish color. In the image the mature sporangia are seen showing below pseudoindusium after unfolding explosively to disperse spores. I recommend to extend the photo with a double click.

Sporangium of Pteris incompleta already unfolded after the dispersal of spores. The torn membrane of pocket where are formed the spores is seen. The spores have been fed by the ring of red fire cells that makes the function of placenta.

Spores of Pteris incompleta measured in microns. They are tetrahedral and muricate, that is to say, with the surface full of thorns or stings.