Plants of the Gila Wilderness

Placidium squamulosum is a squamulose lichen (made up of small scale-like lobes) found on soil. It is dull brown when dry, and bright green when wettened. The undersurface is light brown without obvious rhizines. The cortex becomes translucent when wet, allowing the green algal photobiont (Myrmecia) to shine through. The perithecia (lichens are called pyrenocarpous when the mycobiont sexually reproduces with perithecia rather than apothecia) are usually inconspicuously buried in the thallus and make the lower medulla bulge, but they can also be marginal or in young parts of the thallus and be more conspicuous. Tests for secondary metabolites are negative. We found Placidium squamulosum on dry sand over bedrock in an area where water pools when it rains.
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Placidium squamulosum, photo Russ Kleinman & Karen Blisard, Gila NF, Burro Mtns., Tyrone Thompson Rd., October 23, 2019

Placidium squamulosum, after being wettened, photo Russ Kleinman & Karen Blisard, Gila NF, Burro Mtns., Tyrone Thompson Rd., October 23, 2019

Placidium squamulosum, undersurface, photo Russ Kleinman & Karen Blisard, Gila NF, Burro Mtns., Tyrone Thompson Rd., October 23, 2019

Placidium squamulosum, photomicrograph of cross section of thallus, photo Russ Kleinman & Karen Blisard, Gila NF, Burro Mtns., Tyrone Thompson Rd., October 23, 2019

Placidium squamulosum, photomicrograph of portion of thallus containing young perithecia , photo Russ Kleinman & Karen Blisard, Gila NF, Burro Mtns., Tyrone Thompson Rd., October 23, 2019

Placidium squamulosum, young perithecium, photo Russ Kleinman & Karen Blisard, Gila NF, Burro Mtns., Tyrone Thompson Rd., October 23, 2019

Placidium squamulosum, cross section through young perithecium, photo Russ Kleinman & Karen Blisard, Gila NF, Burro Mtns., Tyrone Thompson Rd., October 23, 2019