DMC #18: Overlooked Super-Survivor
This is the 18th cache of a 20-cache circuit, consisting of 16 new + 4 existing caches adopted from Santos L Helper, which takes you anticlockwise through lovely mixed countryside from near Denton village across to near Middleton hamlet and back.
See DMC #1: Intro & Start for background info on the series, a map (also found in this cache's Gallery) and parking waypoints.
The cache, a small camo-taped tablet pot, is hidden in a log-pile a short distance off the trail as it crosses a grassy area adjacent to the woods.
You may notice some flat growths on the bark of the logs which belong to an amazing and ubiquitous organism, overlooked by most people as they go about their daily lives . . . lichen.
Ancient woods - like West Park Wood, which you passed through twice earlier in this series and nearby Middleton Wood - and abandoned log piles (such as here) are particularly important for lichen as they provide an undisturbed environment where lichen can thrive. Lichens need this as they take a long time to develop, growing only 1-2mm a year.
Some lichen species require alkaline conditions and are only found growing on old bark. Bark can become more alkaline with age, so tree species such as ash – which has a relatively high pH of bark - are home to many lichen species - in fact, some 536 lichen species are associated with ash! [Birch bark is acidic]
All of this really underlines how crucial a single ancient tree or even an undisturbed pile of logs can be for our varied lichen species,.
A lichen (pronounced either as 'liken' or as 'litchen' (like kitchen) is a fascinating composite organism that 
arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship. The fungus requires carbohydrate as a food source whereas the algae or cyanobacteria require shelter. As the algae/cyanobacteria are photosynthetic they provide the food for the fungus in return for that shelter. It's a partnership that works.
Lichens have different properties from those of its component organisms. They come in many colors, sizes, and forms and are sometimes plant-like, but lichens are not plants.
The shape of a lichen is usually determined by the organization of the fungal filaments. The non-reproductive tissues, or vegetative body parts, are called the thallus. Lichens are grouped by thallus type, since this is usually the most visually prominent part of the lichen and common names for lichens often come from a growth form or color that is typical of a lichen genus.
Common groupings of lichen thallus growth forms are:
fruticose – growing like a tuft or multiple-branched leafless mini-shrub, upright or hanging down, 3-dimensional branches with nearly round cross section (terete) or flattened
foliose – growing in 2-dimensional, flat, leaf-like lobes (such as the one seen on the cache tree which is thought to be the Common Greenshield Lichen (Flavoparmelia caperata)
crustose – crust-like, adhering tightly to a surface (substrate) like a thick coat of paint
squamulose – formed of small leaf-like scales crustose below but free at the tips
leprose – powdery
gelatinous – jelly-like
filamentous – stringy or like matted hair
byssoid – wispy, like teased wool
structureless
Common names for lichens may contain the word moss (eg. reindeer moss, Iceland moss), and they may superficially look like and grow with mosses, but they are not related to mosses or any plant.
They do not have roots that absorb water and nutrients as plants do, but like plants, they produce their own nutrition by photosynthesis. When they grow on plants, they do not live as parasites, but instead use the plants as a substrate.
They occur from sea level to high alpine elevations, in many environmental conditions, and can grow on almost any surface. Lichens are abundant growing on bark, leaves, mosses, on other lichens, and hanging from branches 'living on thin air' (epiphytes) in rain forests and in temperate woodland.
They grow on rock, walls, gravestones, roofs, exposed soil surfaces, and in the soil as part of a biological soil crust. Different kinds of lichens have adapted to survive in some of the most extreme environments on Earth: arctic tundra, hot dry deserts, rocky coasts, and toxic slag heaps. They can even live inside solid rock, growing between the grains!
Some 6% of Earth's land surface is covered by lichens and there about 20,000 known species! Some have lost the ability to reproduce sexually, yet continue to speciate. They can be seen as being relatively self-contained miniature ecosystems, where the fungi, algae, or cyanobacteria have the potential to engage with other microorganisms in a functioning system that may evolve as an even more complex composite organism.
They may be long-lived, with some considered to be among the oldest living things. They are among the first living things to grow on fresh rock exposed after an event such as a landslide. The long life-span and slow and regular growth rate of some lichens can be used to date events (lichenometry).
They key players in various environmental processes, eg. nitrogen fixation, biological weathering whereby 
the lichen breaks down rocks to release minerals, and in pollution monitoring (lichen biomonitoring).
See here for more info on these amazing organisms.
Videos: see here for a short introduction to lichens, here for a fascinating short film Lichen in the City, here for lichen timelapse, here for 'For the Love of Lichen', here for studying lichens, and here for lichen diversity & structure.
So, hopefully - for you at least - they will no longer be overlooked!