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. 

Nephrolepis exaltata var. bostoniensis

A beautiful American invader

The Nephrolepis exaltata is one of the garden ferns more cultivated in all the Earth regions with subtropical, Mediterranean and temperate climates without frosts. Their natural habitat is the humid forests and the marshes. It has a great facility to the vegetative reproduction through the emission of exploratory roots, which confers it an invading character that gets to turn it into a true plague when the climate and the habitat are favorable. Like the Nephrolepis cordifolia belongs to the Oleandraceae family. 

Nephrolepis exaltata of the bostoniensis variety, called Wild Boston fern, Tuber ladder fern or Fishbone fern, cultivated in the terrace of a hotel of Funchal city in the Island of Madeira. Their long, wide and turgid fronds showy differentiate from the Nephrolepis cordifolia, whose fronds are narrower and smaller. Extending the photo with a double click can be seen like rhizome has emitted long exploratory roots, of which new ferns bring forth, identical clones of its mother.

Rooting bud of the previous Nephrolepis exaltata var. bostoniensis at the beginning of May. The exploratory roots are seen that they grow looking for new lands and they are emitting rooting buds. 

The same previous roots emitting new buds to more of a meter of distance of its mother.

New frond of one of the rooting buds of the previous image. As it happens with the new fronds of the majority of the ferns, the one of the image it follows the Mathematical Sequence of Fibonacci while it is unfolded. It calls attention its dense off-white hairiness.

The Nephrolepis exaltata is an original American fern of Florida, Mexico, Cuba, Dominican Republic, Haiti, Jamaica, Puerto Rico, Brazil and French Guyana, although it has been feral and naturalized in other American countries with a warm climate without frosts, as well as in other many countries of Africa, Asia and Polynesia. In the Islands of the Macaronesia, especially in the Canary Islands, also it has been feral but it has still not become a worrisome plague. Through culture many varieties have been selected: Bostoniensis, Aurea, Chidsii, Elegantissima, Hillii, Mini Ruffle, Silver Balls, Green Fantasy, Montana, Teddy Junior, Todeoides, Whitmanii Improved, Rooseveltii, etc... The bostoniensis variety is the most commonly cultivated cultivar. This beautiful mutation was discovered in a shipment of Nephrolepis exaltata to Boston from Philadelphia in 1894.

Since I have already indicated at the beginning of this article, all the Nephrolepis has a strong invading tendency, as much through spores as through rooting buds. In the image the trunk of a canary palm is seen, Phoenix canariensis, place setting of rooting buds of Nephrolepis exaltata, arisen all from a unique unit born from a feral spore coming from a near garden, growing like epiphyte between the dried remains of the leaves of the palm. All the rooting buds are united by their roots, being in fact a single individual. The image was taken in a public garden from Orotava city in Tenerife Island.

New frond of Nephrolepis exaltata var. bostoniensis. It calls the attention the great width of its lamina. This detail difference it of the common variety of Nephrolepis exaltata, as it can be seen in the image of the previous epiphyte fern, of narrower and less vigorous fronds something. In the Nephrolepis cordifolia the fronds are even more narrower and shorter.

Frond already completely developed of Nephrolepis exaltata var. bostoniensis. It calls the attention the rachis of a shining brown mahogany color and the long pinnae with crenate edge. The fronds of this cultivar can measure between 50 and 250 centimeters in length and up to 16 centimeters in width.

Giving the return to the previous frond the gorgeous mature cleared sori filled with spores are seen, emplaced in two rows following the edge of each pinna. Pinnae have a short petiole and they are emplaced in alternating form on rachis. In its base they have two cleared auricles that do not get to embrace to rachis. This last detail difference it clearly of the Nephrolepis cordifolia, whose pinnae lack petiole and have two auricles that they embrace to rachis.

 Detail of the basal auricles of pinnae of Nephrolepis cordifolia, that they embrace to rachis and they lack petiole. This so showy difference serves to identify correctly the two more cultivated Nephrolepis in the World. 

Mature sori just before initiating the dispersion of spores. Each sorus is covered by a reniform or cleared-reniform indusium attached to the pinna on its central part as an umbrella that opens towards out allowing that the sporangia unfold and disperse spores. This kidney-shaped indusium gives the name to the sort: the Greek word Nephro means kidney and the Lepis word grudge, that is to say, grudge in the form of kidney, by the reniform form of indusium that covers the sporangia. 

Close-up image of the sori of Nephrolepis exaltata var. bostoniensis with the detail of reniform or cleared-reniform indusium as a umbrella that covers each sorus and it opens towards out. Extending the image with a double click the brown sporangia are seen very well that unfold explosively and disperse spores more far possible of their mother. On pinna are tiny brown small points that they are spores just dispersed.

Gorgeous sporangium of Nephrolepis exaltata var. bostoniensis with short sporangiophore in its inferior part that is stuck to the inferior surface of pinna and receives from it the water and the nutrients to feed spores in formation, which grow within the transparent bag embraced by the ring of cells that have a similar function to the placenta from the uterus of mammals.

Spores of Nephrolepis exaltata var. bostoniensis. Its small size inferior to 39 microns indicates that it is a diploid fern.