Tuesday, January 4, 2011

Xanthoria parietina, the lichen of gold

Xanthoria parietina is a lichen that under conditions of strong sunshine and low humidity has a nice golden color, as if formed by bits of gold leaf glued together as more or less rounded rosette of no more than 10 cms. in diameter. Belongs to the family of the Parmeliaceae.

Usually grows on the bark of trees in nutrient-rich alkaline pH, but his versatility allows him to live on superificies as diverse as limestone, roofing, asparagus and, most amazing, animal bones clean of flesh after putrefaction, by hunger for minerals.

Pelvis bone of a dead sheep colonized by Xanthoria parietina, in a sunny dry scrubland south of the Island of Mallorca. (Double click on the photo to enlarge)
Like all lichens are formed by the intimate symbiotic union between an alga and a fungus. The alga or phycobiont brings energy from photosynthesis, while the fungus or mycobiont provides water and minerals. Many millions of years ago learned to live together, helping each other, allowing them to successfully colonize the new land emerging from volcanic eruptions and tectonic plate movements. In fact, lichens are often the first living organisms to colonize the volcanic islands just after the lava cooled.

Femur of sheep with several Xanthoria parietina that have come together in exuberant growth by nutrient-rich bone. Particularly striking is the lack of growth in the non sunny bone, by the need for sunlight of symbiotic algae, whose chlorophyll depends on sunlight for photosynthesis.

The other femur of the same sheep with Xanthoria parietina only on the side facing south. Note the extreme aridity of the garrigue soil, cracked and scorched by the hot summer sun of Mallorca. These harsh conditions do not appear to have any effect on lichen, quite the contrary, by its acute heliophilia and thermophilia.

Greater trochanter and lesser trochanter covered by lichen. On the head of the femur can see two tiny Xanthoria parietina newly germinated. Double click on photo to enlarge it, you see the orange apothecia fruiting bodies that are developed by the fungus or mycobiont, which produce ascospores for sexual reproduction. The alga or phycobiont can not reproduce sexually and his cells called gonidia are attached to the ascospores, so that when they germinate and form hyphae or fungal filaments in a network, the algae cells are placed in the hollow of the hyphae growing together in symbiosis.

Xanthoria parietina covering the south side of the bark of a young pistachio, Pistacia vera, in the middle of August, in an orchard in the Valley of Soller on the island of Mallorca.

Xanthoria parietina pistachio same earlier in the month of December with the detail of their fruiting bodies or apothecia. (Double click on the photo to enlarge)

Curious growth of Xanthoria parietina on the internodes of Asparagus albus, in the property Na Riera  of Algaida Village, located in the center of the Island of Mallorca.

Beautiful Xanthoria parietina growing on the roof of PVC in a greenhouse in late December.

Xanthoria parietina growing on Echinopsis atacamensis ssp. pasacana in the magnificent Botanicactus of Ses Salines in southern of Mallorca.

Young Xanthoria parietina on the bark of Acer negundo a greenish color to grow in the shade of the bark of maple with a lot of humidity.

Close-up image of Xanthoria parietina growing on the same maple of previous photo with the detail of the apothecia of mycobiont at different stages of maturation. (Double click on the photo to enlarge)

Vigorous Xanthoria parietina with lush growth on the bark of an elder tree, Sambucus nigra. The intense green color is due to the humidity of the porous elder tree bark, which acts like a sponge, retaining rainwater, so get a hearty lichen water intake. 

And finally in this picture you can see a group of Xanthoria parietina growing on a moist, shaded boulder in a thick oak forest of the Serra de Tramuntana in Mallorca. It is appreciated that acquires greenish lichen in these wet conditions and poor light.

This lichen was used in ancient pharmacopoeia for treating malaria with the name of lichen parietinus as a substitute for cinchona bark. It was also used as a dye for dyeing yellow and brown because it contains parietina.

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