Sunday, June 5, 2011

Sticta canariensis, a bigamous liquen with a green wife and a blue one

 In early May, I was descending the steep path of Taganana Turns in the Parque Rural de Anaga located on the northern tip of the island of Tenerife. I went obsessed looking for Asplenium x tagananaense, a rare hybrid fern between Asplenium hemionitis and Asplenium onopteris that around the world is only found in the Anaga massif. In the shady understory of that earthly paradise covered by the high canopy of laurel trees were hundreds of beautiful ferns, but none was Taganana hybrid. Scanning with the view each and every one of the ferns I noticed a very curly endive kind of a nice bright green color. Clinging to the branches of the bushes, climbed a hill on whose floor was a thick layer of humus. When I had the proper footing and I could free my hands, I took my dear compact camera and I made several photos at the giant lichen, the largest I had seen in my life. A few days later, at home, I got to know his identity: Sticta canariensis. (I recommend you double-click on this and the following pictures to appreciate its size and details.)

A lichen is a symbiotic union between a fungus and an alga. For better understanding, we can say that this union becomes a kind of marriage of convenience in which both spouses make a profit. The fungus or mycobiont may be an ascomycete or a basidiomycete, although in most lichens the fungus is an ascomycete. Some ascomycetes fungi can live as independent beings or associated with algae to form lichen. Other ascomycetes can only live as lichens associated with an alga. The transition from independent fungus to symbiotic fungus is considered an advance in evolution, since the association with an alga is very beneficial for the survival of the fungus.

As for the other component, the alga or ficobiont can be a green alga or a blue alga, also called cyanobacteria. The most significant difference between them is that green alga can only perform photosynthesis like any plant, while the cyanobacteria or blue alga has taken a further step in the evolution and besides photosynthesis it is also able to fix atmospheric nitrogen with which provides a valuable component of the symbiosis. This ability to fix nitrogen from the air is of great importance in the formation of fertile soil in the new land emerged after a volcanic eruption.

Almost the entire structure of a liquen is formed by filaments or hyphae, between which are located the unicellular algae. Their union is so intimate and coordination between the two symbionts is so perfect that are able to grow and live as if they were a individual living. The fungus provides water and minerals from the soil, while green alga contributes carbohydrates of fontosíntesis. In the case of blue algae also provides atmospheric nitrogen.

 Image of part of the lichen Sticta canariensis photo above, which are really three copies growing together.

Each component of the union is reproduced separately. The fungus makes it through spores and the algae by simple cell division. However, to form a lichen both symbionts must be in the right place at the right time. The fungus spore germinates if it falls on a substrate with sufficient moisture, but if in that place there are not adequate algae cells the fungus spore die, except if it is an ascomycete able to live alone without an alga. If, however, if near the spore that is germinating there are some algae cells the fungal filaments surrounding the algal cells and start living together. Birth of a lichen.

The high humidity of the understory, the subdued light and the rich substrate decomposed leaves allow it to grow so lush. Without exaggerating copy of this photo was rounded appearance and size of an endive salad.

The ascomycete lichen Sticta canariensis has taken a step in the evolution and achieved two algae associated with different depending on the degree of cold in the region where it grows. In the northernmost regions tends to be associated with blue algae or cyanobacteria leading to a lichen Sticta dufourii color varies according to humidity, sunlight, substrate type, etc ... that can range from pearly beige, green more or less dark gray, brownish or even to black. In the warmer southern regions tend to associate with a green alga leading lichen Sticta canariensis. Sometimes in the intermediate regions are specimens with parts of Sticta dufourii and parts of Sticta canariensis. Would be more like a hybrid lichen.

 Sticta image with parts with green alga and parts with cyanobacteria. It is owned by photographer Ray Woods. I found this great website dedicated to the world of lichens: Lichen Apprentice Scheme Wales

Both species or symbiotic associations are distributed through western Europe and Macaronesia. In Norway and the British Isles dominated the partnership with the blue alga, Sticta dufourii, while in Macaronesia dominated the association with green algae, Sticta canariensis.

 A close-up image allows us to appreciate the apothecia or ascomycete fruiting bodies, where they form spores for reproduction. The algae do not need reproductive organs, because as we have seen is reproduced by simple cell division. Often several cells of the algae stick to the spores of the fungus, so they are easier to disperse much reproduction of the lichen.

Details of the apothecia of the ascomycete red cup shape. All the lichen was soaked in moisture and shines in the darkness of the undergrowth.

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