Wednesday, November 30, 2011

Diploschistes diacapsis likes that they trample it

The lichen Diploschistes diacapsis was everything a discovery for me. That one behind schedule of autumn walked behind the prestigious botanist and excellent friend Juan Rita Larrucea, between rockroses, mastics and rosemaries. We went towards a temporary raft located in a coastal Garriga of the southwest of Majorca to see the small population of the aquatic fern Marsilea strigosa that was for me a pending subject. Juan had amiably offered itself to teach it to me.  

I recommend to extend the photos with a double click.

While we crossed clear of Garriga with little vegetation and calcareous rocks showing itself over the thin argillaceous earth layer, suddenly I noticed that Juan lessen his step and watched my feet after the tip of the eye. Account had occurred that I avoided to step on the lichens and he was leaving behind to me. Smiling it said to me: " Nonsubjects, not them beams no damage if you trample. These lichens specifically grow in the sites of passage of people and animal, because when stepping on they are divided them and each piece is a new lichen that continues growing. It is its form to reproduce vegetative by fragmentation". 

The illusion to see the Marsilea strigosa for the first time in my life did not prevent me to waste a little time in contemplating that one wonder of the nature that had adapted intelligently to the trampling of the cattle. I crouched and I took several photos with my old digital camera to take them to me like memory of that one full day of surprises that Juan had given me, because one hour before in another Garriga had taught another tiny fern to me that was also a pending subject for me, the Ophioglossum lusitanicum.

Already without fear of trample those white lichens that I had not seen before in my life, I felt as they creaked and they fragmented under my shoes. I removed the ball-point pen that ground to always take in the pocket of the shirt and I wrote in the palm of my hand the complicated name of the lichen that Juan had spelled to me, Diploschistes diacapsis. As soon as it arrives at house, I thought, I will look for information in google and an excellent Guide of Lichens, Mosses and Hepatics that I bought in Jerez de la Frontera several years ago. 

Diploschistes diacapsis very fragmented after the passage of a flock of ewes. 

The Diploschistes diacapsis, also call Diploschistes steppicus, usually grows to total sun applied on carbonated or chalky substrates. In Majorca it lives on very poor argillaceous grounds with little rains and a strong insolation. Sights by far these lichens seem outcrops of calcareous rocks excelling millimeters over the earth layer.

The body of the lichen, that is to say, the white plate receives the thallus name. Usually it has a thickness of about 2 millimeters and gets to measure up to 20 centimeters of diameter. Its surface is irregular, warty of white color with tonalities beig or clear gray and sprinkled of black or grayish small points in the form of tiny discs very sunk in the thallus called apotheciums. Sometimes parts of the thallus are separated of the ground leaving hollow.

A lichen is the symbiotic association between a fungus and an alga. The apotheciums are the reproductive organs of the symbiont fungus called micobiont. In each apothecium are small bags called asci, where the greenish or brownish ascospores in number of 8 by each ascus. After an abundant rain the asci reach the maturity quickly, become very turgescent and explode, releasing the ascospores explosively to the air so that they arrive more far possible.

Detail of the apotheciums in different stages from maturation. They begin punctiform and little by little they are been high and mighty and sinking in the thallus, forming small craters.

The other component of the lichen receives the name of ficobiont and is formed by unicellular algae that lives in very little number in the ground. In conditions of extreme aridity the algae only can survive associate a fungus forming a lichen. After an abundant rain some cells algals are freed of the fungus and fall in the small pools where they reproduce like any alga. Its aquatic life is very brief. If the pool is dried, the alga dies. Not to be extinguished they resort to the intelligent strategy to be associated to a fungus.

When an ascospore is dispersed by the outbreak of a ascus flies more far possible helped by the wind and if it falls on a suitable humid substrate it germinates and it begins to produce a filament maze or hyphae. Nevertheless, if it soon does not find an unicellular alga with which to be associated, the fungus literally dies of starvation when needing it the carbohydrate contribution synthesized by the chlorophyll of the alga. 

When there is luck and the chance causes that both simbionts are in the same point where fell the ascospore, generally a small accumulation of rainwater in the ground, as hyphae of the fungus is forming a filament maze, that is to say, the structure of the lichen, the unicellular algae are reproduced by simple cellular division and the new cells algals are placed between hyphae in intimate contact with them, as if renters of a building it was. The true symbiosis begins then. Fungal hyphae absorbs water and minerals of the ground and transfer them to the algae. These in return provide to hyphae of the fungus the carbohydrates that have elaborated from the solar light. They form because a reconciled marriage of good convenience in which both spouses remove a benefit. Really, they represent an intelligent strategy of survival of two beings who separately could not survive.

It is therefore understood the need for this lichen to be trampled, as vegetative reproduction by fragmentation of the thallus is much easier and safer than random reproduction by spores in a habitat where rains are very rare and extreme dryness prevails over most of the year.

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