Canoerebel
Posts: 21100
Joined: 12/14/2002 From: Northwestern Georgia, USA Status: offline
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You gents need soothing reading about things botanical. I wrote this after a hike a few weeks ago: Symbionts The toe of a woodland ridge I walk nudges a creek, then ranges up to a shallow gap between two knobs. Lichen-speckled boulders jut from the slanting ridge spine, like gray, humped-back whales broaching sea swells. If together we walked that ridge, moving among the rocks, and I queried, “Do you know what a lichen is?” you’d nod, pointing to pale-turquoise growth dappling each boulder. If curiosity lingered, you might probe further, inquiring: “But what is a lichen, really?” as once I did. We know lichens by sight – common plants growing on exposed rock or soil, bark, limbs, gravestones, sidewalks, walls, roofs, and even on other lichens. They’re often papery thin, as if flour and water mixed into paste and brushed on an object were allowed to dry, the edges then folding and scalloping irregularly. But the science of the matter confounds, for a lichen isn’t a plant at all. It isn’t even an organism. More precisely, it isn’t a single organism. An old-timer once explained lichen science to me. A student of natural history and woodland lore, he pointed to a specimen on a boulder and said, “Lichens are a symbiotic relationship [a what?] between an alga and a fungus.” A lichen, he expounded, is two organisms coexisting, dependent each on the other – an alga using water and minerals absorbed by a fungus to produce food by photosynthesis, which feeds both life forms. The two organisms can exist independently, as alga and as fungus, but a lichen exists only when they live together, mutually dependent on one another. Scholars dub states of mutuality among living things “symbiosis.” The alga and the fungus are “symbionts.” Science organizes all known lifeforms into five biological kingdoms. The organisms that make up lichens aren’t from the familiar Plant or Animal Kingdoms, but each of the other three kingdoms is involved. Every lichen consists of a member of the Kingdom Fungi living in association with either a member of the Kingdom Protista or the Kingdom Monera. Blue-green algae and a fungus comprise many common lichens, creating the faded turquoise coloring – as if the lichens had been exposed to overmuch sunlight – so familiar on northwest Georgia’s rocky ridges. But blue-green alga really isn’t an alga, so it isn’t a member of the Kingdom Protista. It’s cyanobacteria from the Kingdom Monera – bacteria capable of photosynthesis. Lifeforms from different kingdoms living together symbiotically might be comparable to turtles living in trees, if the two depended one on the other so much that they became as one and were so perceived by mankind. There are twenty thousand species of lichen (“species” really isn’t the right term since organisms from multiple kingdoms are involved). Lichens are delicate but have adapted to earth’s most hostile environments – tundra, mountains, deserts, and toxic slag heaps. They’re hardy and opportunistic, covering about nine percent of the planet’s surface. The day my friend asked, “Do know what a lichen is?” as we walked the gnarled-rock spine of Taylors Ridge, I replied, “Sure,” and pointed to a rock colonized by faded turquoise growth illuminated under a cloudless winter sky’s brilliant blueness. Oh, yes, I could point to a lichen, but I did so without knowing its simple, marvelous complexity.
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