Freitag, 21. März 2014

Species of the Day (March 21st; 2014) - Stereocaulon vesuvianum (Sm.) Ach.

Today's “Plant of the Day” isn't a real plant but a lichen. This lichen is Stereocaulon vesuvianum (Sm.) Ach. from the Stereocaulaceae Family. The species has no common name but the literally translation of the species' name means “Mount Vesuvius Stereocaulon” in English (“Vesuv-Stereocaulon” or “Vesuvflechte” in German).

1) Description

S. vesuvianum is a flat lichen. The greyish-green to green Thallus grows flat on the substrate at the beginning but erects later with many branches, which are about 4 centimeters high. These branches are irregularly shaped and grows in any direction. As a result, the habitus of S. vesuvianum reminds to the smoke clouds from an erupting volcano like Mount Vesuvius. This is also the reason for the name “vesuvianum”. 

 S. vesuvianum - on a stone

These “branches” are more long protrusions of the cells of the Thallus and not a real ramification. In Lichenology, such a structure is called a Pseudopodium. In the case of S. vesuvianum these branches have a greyish color with a small touch of orange (what reinforce the impression of a volcano).

S. vesuvianum - habitus

Soredia (small, clustered fragments of the Thallus) are located at the end of the Pseudopodia. They serve for asexual reproduction by breaking off from the lichen in order to form a new Thallus. Many lichens prefer this way of reproduction over the sexual reproduction by spores. Especially under tough conditions, an asexual reproduction is much easier than a sexual.

S. vesuvianum - you can see the pseudopodia

Apothecia are rare. However, if they are present, they are also located at the apices of the pseudopodia, where they create spores for the sexual reproduction. The measurements of these spores are about 40 X 3,5 µm, so they are much longer than hight. The spores are also septated in 3 to 5 sub-sections.

2) Distribution and Ecology

Despite the name, S. vesuvianum isn't endemic to the regions around Mount Vesuvianus. The species is a cosmopolitan and very common in both hemispheres. So, it can be found in Europe, but also in Asia or Australia. S. vesuvianum prefers siliceous and acid substrate and grows on rocks, walls or gravel.

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