|Color code :||
|Translations :||NC, NC, Algue, NC, NC|
|Definition :||Algae are microscopic vegetal organisms without stem nor leaves which can be seen outdoors and indoors, as powdery or viscous deposits (thickness : tenth of mm to several mm). Algae form green, red,brown, or black veil like zones and can be found mainly in situations where the substrate remains moistened for long periods of time. Depending on the environmental conditions and substrate type,algae may form solid layers or smooth films. On monuments, algae are constituted of unicellular to pluricellular clusters, and they never form macroorganisms.|
|Relationship with the substrate :||Algae generally constitute superficial films. They may be found also deeper into the substrate (under scales, in cracks).|
|Equivalent terms to be found in other glossaries :||NA|
|Other orthograph :||Plural form : algae.|
|Not to be confused with :||Algae may be confused with epilithic lichen, with fungae and
sometimes with soot or mineral deposits soiling the stone surface.
If algae are present, wetting and brushing the surface
will turn it to green due to the presence of chlorophyll.
|Other remarks :||Several groups of algae may grow on and in stone depending
on climate and stone type. Green algae (sometimes red, e.g.
trentepohlia) diatoms (usually yellow to brown), and in rare
cases red algae may occur. Cyanobacteria (formerly called
blue-green algae) are very frequent stone dwellers and can
cause black, bluish or even violet stains.
In some cases the stone serves as a source of nutrients.
However usually the stone surface is only a solid host for
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