Lichen looks like a plant but is not scientifically classified as one. It’s a combination of a fungus (which is not a plant) and an alga (also not a plant). The fungus supplies a place to live for the alga, which has chlorophyll and photosynthesises like a plant, so supplies both of them with sugars and other nutrients – win/win.
This lichen’s from Barker’s Vale, up the road from me …
as is this one …
Lichen are useful environmental monitors – if you’ve got them, you know the air is clean. They rapidly disappear when pollution’s about.
There’s a way of telling how old a lichen is (‘lichenometrics’). I’ll quote from Richard Fortey’s book about the British Museum of Natural History, ‘Dry Storeroom No. 1’, as he puts it way better than I could. (The book is great, by the way – the man, a world authority on palaeontology, joined the BM in 1970 and has now retired but still continues his research, as do many retired BM-ers. He describes with wit and intelligence the more interesting exhibits, the scientists (some very eccentric) and the behind-the-scenes doings of the museum. I used to work in the SA Museum of Natural History, so could relate to much of it, although the details were, of course, very different. Anyone who likens the BM to Gormenghast wins my vote.)
Many lichens … grow very slowly, some just a few millimetres a year, and some even less than a millimetre. It is an interesting problem how to determine this rate of growth. One way … is to use gravestones. … A gravestone includes that very useful piece of information – a date. When erected they are pristine, but soon time and lichens make their mark. Lichens on flat gravestones tend to grow outwards in a regular circle, so the diameter of the circle is proportional to its age. The largest circle found on a gravestone of a particular date will give an approximation to the maximum rate of growth. There will be a certain range of variation as a consequence of local conditions, and variation in the time of first colonization. Furthermore, as time passes, new species of lichen will join the gravestone habitat – and younger rings will ‘cut’ through the older ones as they grow, so revealing the order of succession of colonization. A good gravestone will accordingly yield a complex narrative, and many gravestones will provide usable statistics. Rates can then be applied to other sites.
Now me, I like hanging around in graveyards. As a kid I used to amuse myself for hours looking at the wildlife in my country town’s local one – it was the only place with decent trees and shrubs and that was quiet and mostly people-free (at least from living ones). But that cemetery is only 140 or so years old. When I got to England in 2008, I was happy to spend a morning at Madron parish church (St Madrona’s) in Cornwall. It was built about 1500 AD so the lichen was well-progressed. Unfortunately the building was locked, so I couldn’t admire the inside.
Graveyards have a lot of history, if only you can read the dates and inscriptions. In Moonta and Kadina, copper mining towns in South Australia which attracted many Cornish tin-miners, I saw many gravestones of children who died from a measles epidemic in the early days of mining. Finding this kind of history yourself is fascinating, and has much more impact than merely reading about it in history books.
Unfortunately many of the inscriptions in Madron were unreadable. I guess someone somewhere has written a book or paper on fashions in English gravestone styles and the years they became popular. That would help. I’ll just show some of the more interesting ones, without any details about age.
While writing this, I ‘googled’ my childhood graveyard (sounds a bit Buffy the Vampire Slayer, no?), and was disappointed to see that it has been spruced up rather a lot. Rather than a quiet, run-down place on the edge of town, suitable for a budding naturalist, it’s now surrounded by suburb, clean and tidy and with a lot more, ahem, inhabitants. Ah well, that’s progress, I guess.