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A Glimpse of Nature -- Together

As several readers noted, last week’s “What Is It!” was a lichen, one of those extraordinary partnerships between a fungus and an alga. I am sure many of you have seen it on the library’s Main Street wall. Yes, that yellow “paint” is alive!


Lichen on Library Wall, January 2023

Most readers, even those with a passing interest in nature, will be familiar with the lichen version of symbiosis wherein a fungus lives in association with a photosynthetic partner (an alga and/or a cyanobacterium). The fungus provides the structure through a body called a thallus; the alga provides nutrients in the form of carbohydrates. By living as one organism, the lichen can survive in environments that could not support its components, even in tough habitats that lack water or nutrients . . . such as rock walls.

All the same, this simplified explanation implies that the two species are merely roommates, each retaining its own identity when, in fact, their association creates something entirely different. I like how William Purvis compares them to “mini-ecosystems” in his book, Lichens (Smithsonian University Press). He stresses that this association of species from different kingdoms results “in a distinct lichen body (thallus) being formed [which] looks very different from the individual partners when they are separated and grown in laboratory cultures.” Both organisms are transformed. Indeed, the alga loses its cell walls and can no longer reproduce itself. Yet, as Purvis explains, the “photobiont” partner can dramatically affect a lichen’s shape, causing it to be leaf-like or shrublike in appearance.

Not surprisingly, such complex organisms are difficult to identify. Some lichens may be recognized in the field, while others require microscopic and chemical analysis for identification. To the best of my (very limited) knowledge, our yellow lichen is in the Candelariaceae family; perhaps one of the candleflame lichens. This family of lichen-forming fungi contains “about 73 species” according to Wikipedia. I would prefer to be more precise.


All the same, I enjoy finding and examining lichens, especially with a good hand lens, and I encourage you to do the same. They grow almost everywhere – on trees, rocks, bare soil, headstones, sea cliffs, roofs, etc. – and they are conspicuous in winter. Begin by grouping your finds by general form. Is your lichen lobed and leaf-like with a top and bottom side? That structure is called foliose.


 Foliose Form

If it is pressed tight against its substrate, it is crustose.


Crustose Form

Lastly, if your lichen is branched, hairlike, shrubby, or cuplike, it has a fruticose growth form.


Fruticose Form

This chart from the National Park Service compares the forms.


 Next week, we’ll dig deeper into lichen biology and consider some representative species. ‘Til then, I challenge you to find and photograph three lichens, one with each of the growth forms illustrated above. If you send your images to A Glimpse of Nature, they might appear in next week’s post.


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Submitted by louis john on

fascinating, I will look again... and again

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