Christella dentata: born to survive

While it is extinguished in Spain, it invades new territories.

Christella dentata fern, also called Cyclosorus dentatus, Cyclosorus nymphalis and Thelypteris dentata, has an ample tropical and subtropical distribution, especially in Australia, New Zealand, Polynesia, sub-Saharian Africa, Madagascar, arriving in its more northern limit at the Macaronesia Islands (Azores, Canary Islands, Madeira, Cape Verde), south of the Iberian Peninsula, south of Italy and Crete.

The facility of its culture as garden plant has allowed it disperse its spores and become feral in new territories with a favorable climate, especially in America. In Hawaii it was introduced in 1887 and in few years become feral with as much success that now is one of the most abundant ferns in those islands. It hybridizes with relative facility with the endemic Christella cyatheoides, giving rise to a sterile triploid hybrid.

  Christella dentata growing in a humid and shady precipice in the North face of Monte Carneiro located in the Island of Faial of Azores Archipelago. In its around can be seen a carpet of leaves of the allochthonous American feral Tradescandia fluminensis.

In year 2002 it extinguished the unique well-known population of Christella dentata in the Iberian Peninsula, concretely in Los Alcornocales Natural Park of Cadiz, closely together of the Straits of Gibraltar. The technicians of the Council of Environment of Andalusia knew that the last well-known units were in very bad state, very debilitated, without hardly bringing forth new fronds and with the old fronds very aggravated. To the being a fern with rhizome crawling very resistant that sprouts again with facility after losing the fronds when the conditions of humidity and temperature return to be favorable, trusted that thus it happened, but that one year 2002 when they went to verify its state no longer they found no Christella dentata. Their fronds and rhizomes were had decomposed and had disappeared between the mulch leaves of the underbrush.

Christella dentata was originated like species in the Tertiary. Its maximum expansion took place when Europe enjoyed a warm and humid tropical climate ebullient forests. The later progressive cooling of the European climate went extinguishing to the Christella dentata of the north towards the south it forced and it to shut in the laurisilva forest of the province of Cadiz, resemblances to those of the Macaronesia, with a permanently humid subtropical climate.  

Years before already one had extinguished in Galicia the other well-known peninsular population of Christella dentata that grew next to thermal upwellings on granite walls in the province of Orense. The thermal hot water had allowed it to survive almost miraculously during million years, while to its around their same types disappeared thundered against by the cold and the drought. 

Therefore the Iberian Christella dentata no longer existed, had been extinguished irremediably. Nevertheless, after the initial deception, the Andalusian technicians reacted, they did not occur by won and they wanted to prove a last and desperate resource. In November of year 2002 they gathered the superficial substrate of the land where the last gaditana population had lived they took and it to the Laboratory of Vegetal Propagation of the Breeding ground of San Jeronimo, whose technicians, advised by scientists of the University of Valencia, seeded that one substrate in means and conditions of ideal temperature and humidity for the hypothetical germination of spores of Christella dentata that could have still viable.

The shrewdness of the Andalusian technicians bore its fruits and after two years, in September of year 2004, the longed for miracle took place. Tiny Christellas appeared between the maze of fungi, mosses, seaweed and other contained ferns arisen from the numerous ones and varied spores in the substrate. They were so small that they had to wait for seven months to that they grew to take samples of its fronds and to analyze them to confirm its identity.

Young Christella dentata cultivated in the Aljibe Botanical Garden located in Alcala de los Gazules in the province of Cadiz.

When they reached the maturity, the technicians cultivated its first spores and obtained numerous units, so that in April of year 2006 they could seed in its old habitat the ten first Christella dentata saved of the extinction. The repopulation was a full success. At the moment the seeded units add several dozens and to protect so appraised treasure the exact location stays privily. They are in a private property whose proprietor collaborates actively in its conservation.

Once assured a stable population in its natural means, the Andalusian Government came to still more send to several units of Christella dentata to all the botanical gardens of Andalusia, they cultivated so that them and they kept spores in their banks from germ plasm, thus guaranteeing its survival.

Tender frond of previous Christella dentata. Call the attention its intense clear green color that it is darker in the adult units. 

 In the low part of this image an adult Christella dentata is seen partially cover by an Athyrium filix-femina. The photo was taken in Monte Carneiro located in the Azorian Island of Faial. Next to both ferns an invading species can be seen, Hedychium gardnerianum, an original garden plant of the Himalayas that in the Azores has been feral with as much success that, like in New Zealand and Hawaii, has finished turned into an uncontrollable vegetal plague. 

Same previous Christella view of fence. In the frond can be seen the detail of the two basal pinnae whose apexes go upwards drawing a wide V, whereas the others pinnae are in a same horizontal plane. Also call the attention the acuminate or caudate end of the lamina, which is narrowed abruptly and finished in a length and pointed apex. Lateral pinnae also has the apex acuminate or caudate. Another showy detail is the so large central pinnae major with respect to the basal ones. In the fronds of the young units these details so are not defined.

Frond of a young Christella dentata of an alive green color clearly. Call the attention the gray rachis of the lamina that is green in the apex and is progressively darkening as it approaches the petiole, which is almost black. The two basal pinnae are seen smaller and arranged in the form of wide V. The fronds can surpass the 70 centimeters in length.

Rachis of almost black very dark gray color that is continued with the petiole of the same color. As the rest of the frond is covered with hairs or tricommas.

Linear-lanceolate and acuminate pinnae of Christella dentata. The margin is cleaved so that the divisions arrive in the middle of the limbo (pinnatifide) either deepen a little the more without arriving at rachis (pinnatipartite). The sights are had oblique on rachis pinna and have the cleared apex.

New frond of Christella dentata at the beginning of May.

Mature sori at the end of December.

Christella dentata sori are orbicular and are located on the nerves of the sights, equidistant of the margin and the average nerve. Indusium is reniform and is covered with rigid hairs. In the photo one does not see, because one has already risen to allow that the sporangia unfold and disperse spores.

Previous sori in which indusium is seen already dry and dissuaded and the showy sporangia like small black balls. The hairs or tricommas can be seen coverall on rachis of pinna and the nerves of pinnules. 

Microphotography of mature sori with the sporangia in the heat of dispersion of spores.

Sporangia of Christella dentata seen the microscope to 400 increases. The bag is transparent already still torn contains spores.

Another sporangium of Christella dentata with the transparent bag already completely torn and empty.

The hairs or tricommas that cover the lamina in all their surface can be short and long. In the photo a long tricomma seen the microscope to 400 increases. 

Short tricomma of Christella dentata with a spore.

Papillose spores of Christella dentata measured in microns.