PINK EARTH LICHEN

The Pink Earth Lichen, Dibaeis beomyces, can be recognized at 40 miles per hour, it’s that distinctive. But, you can be forgiven if you do not immediately recognize it as a lichen.

This lichen forms on sandy mineral soils and clay soils, often at roadsides. It is common and widely distributed in eastern USA and Canada, and Europe, reaching into the Arctic.

A lichen is the symbiotic relationship between a fungus and a green alga or a cyanobacterium. The alga, also known as the photobiont, produces nutrients through photosynthesis and these nutrients are translocated into the fungal cells. The fungus produces protective tissues within which the algal cell nestle; the fungus also produces spores that can disperse the lichen. The thallus, or body, of a lichen comprises fungal and algal cells. The thallus of Pink Earth Lichen is in the form of a crust of algal and fungal cells on the surface of the soil. The little pink mushroomy things produced by this lichen are fungal fructifications.

The fungus fructification of D. beomyces is known as an ‘apothecium.’ The pink, turban-shaped part of the fructification is completely covered by spore producing cells that, as is typical of an apothecium, are completely exposed.

_{In this picture the spores will eventually be produced in the long, club-shaped cells called ‘asci.’Each ascus contains only one, diploid nucleus which resulted from the fusion of two haploid nuclei in a specialized c ell that supports each ascus. The narrow filaments surrounding the asci, ‘paraphyses,’ are sterile; they provide support and protection for the asci.}

Fungi are haploid organisms. This is in contrast to other eukaryotic organisms, including humans and plants, that are diploid. That is, in humans, chromosomes derived from each parent are present in each cell: those cells are diploid. Whereas in fungi, each cell only has the chromosomes from one or the other parent: those cells are haploid. The diploid phase of a fungus is very brief, comprising only one diploid nucleus in each of the fertile cells, and that nucleus quickly undergoes meiosis (reduction division where genetic recombination occurs) to produce, once again, haploid progeny, typically 8 nuclei. A spore forms around each of the 8 haploid nuclei; the spore germinates to produce its thallus, known as a mycelium — narrow filaments that colonize the substratum and bring in nutrients.

_{On the right an ascus with 8 ascospores in an asucs. On the left a closer image of the sexual spores within an ascus.}

Lichens can reproduce through the formation of asexual propagules of various sorts. These are formed of mixed algal and fungal material and can reconstitute the lichen symbiosis. The spores, however, are not dispersed with algal material. The germinating spore must find a compatible algal cell in order to reconstitute the lichen.

The photobiont of Pink Earth Lichen is a green alga in the genus Coccomyxa. It is single-celled, but masses of cells loosely adhere to each other to form the crustose thallus of the lichen.

_{The green in this picture is the crust of cells of the Coccomyxa photobiont}

_{The picture on the right shows masses of green, photosynthesizing Coccomyxa cells. The picture on the left shows four individual Coccomyxa cells, each with what is probably a large lipid drop.}