symbiotic relationships

ERNST HAECKEL

"Lichens are a symbiotic relationship between a fungus, which builds the body of the lichen (the ‘thallus') and encapsulates a population of algae or photosynthetic cyanobacteria. The main bulk of the lichen is composed of fungal material, which harvests food from its symbiotic partner in the form of photosynthetic sugars. There are an estimated 20,000-30,000 species of lichen worldwide, occupying a vast array of terrestrial and semi-aquatic habitats. Lichens are nature's extreme survivors, and are found on every continent - from the coldest parts of Antarctica, to the driest deserts, to the wettest rainforests, to the highest mountains. Despite this resistance to natural environmental extremes, lichens are sensitive to environmental perturbation, and are used as bioindicators for pollutants, climate change, and in habitat management. Lichens play an important role in the establishment of succeeding (i.e., sequentially following) organisms such as mosses or vascular plants. The bulky tissue of the lichen (particularly the thallus, or body) slowly traps air-borne dust and silt, while the fungal hyphae of the lichen penetrates and helps etch a thin layer of the rock's surface. The fine particles of soil in combination with dead or decaying lichen tissue form a medium where moss spores or vascular plant seeds can establish and grow. Over a long period of time (assuming no mechanical disturbances), a layer of mosses and herbaceous plants will replace these lichens. *Although the period of time may be measured in decades or centuries, it is essentially an instant in the scale of geologic time."

it was my cliff walks around Polzeath and the trip to St Ives that made me think about lichen again

*"the scale of geologic time", huh. . . we don't live our lives in that time scale, do we**

**we live our lives in the minutes and hours it takes to walk thru a wood on an autumn afternoon. . .

I hope you have a wonderful afternoon