Botany Photo of the Day

Nebulagirl posted today's Botany Photo of the Day in our Flickr Pool two weeks ago. She included a number of great shots in addition to this close-up, all of which you can access here. Of course, we extend our thanks to nebulagirl for this opportunity to take down and dust off our old lichen-related volumes.

Cladonia cristatella is just one of the planet's over 14000 lichen species. Unlike most plants, lichens are composite organisms; they develop, that is, from a symbiotic association between a unique fungal species and a photosynthetic partner (often green alga or cyanobacteria). They have no hydration apparatus, and this allows them to excel in conditions and habitats fatal to most other plants (deserts, arctic tundra, bare rock and sterile soil). Lichen species' capacity to adapt to the labile complexion of their surrounding environment is perhaps best demonstrated by their ability to enter metabolic suspension (dormancy) in order to survive desiccation in periods of intense water deprivation, proceeding to rehydrate and thrive when a supply of water again becomes available. Though they often grow on other plant specimens, lichens are not parasitic, and they have little, if any, adverse affect upon their host; some species, particularly those in the subgenus Cladina, do, however, emit into the soil chemicals that inhibit, or even preclude, the growth of competing plants. Historically, parts and extracts from lichens have served as ingredients in dyes and perfumes, and they have been thought effective treatments for lung disease and rabies. Generally speaking, humans have not made standard fare of lichens, as most species have a bitter taste and little nutritional value.

In today's photo, Cladonia cristatella (British soldier lichen) seems to ooze from its decaying woody host like fresh magma bubbling up from the coarse veins of the ocean floor. The species joins the Cladonia fungus and the Trebouxia erici alga. A thin stalk lifts the red, club-shaped apothecia up to a height of about 25 mm. This is eastern North America's only red-fruited Cladonia species lacking in both soredia and granules (typical reproductive structures). Unlike other lichen species, Cladonia christatella is somewhat tolerant of pollution, and this is why, in urban areas, it is more common than its relatives.

Source:

Brodo, Irwin, Sylvia Duran Sharnoff, and Stephen Sharnoff. Lichens of North America. New Haven: Yale UP, 2001.