Plants of the Gila Wilderness

Physcia callosa is a whitish lichen that grows on rocks. The undersurface of the thallus is also whitish. The small, narrow lobes of the thallus are somewhat ascending and shed grayish soredia on downturned margins. Soredia are asexual propagules consisting of a group of algal cells surrounded by fungal filaments without a covering of cortex. P. callosa is pruinose-- there are whitish granules on its upper surface. The cortex (but not the medulla) is yellow in KOH.
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Physcia callosa, photo Russ Kleinman & Karen Blisard, Pinos Altos Range, Pinos Altos, April 12, 2018

Physcia callosa, growth habit, photo Russ Kleinman & Karen Blisard, Pinos Altos Range, Pinos Altos, April 12, 2018

Physcia callosa, photomicrograph of thallus, photo Russ Kleinman & Karen Blisard, Pinos Altos Range, Pinos Altos, April 12, 2018

Physcia callosa, photomicrograph of thallus, photo Russ Kleinman & Karen Blisard, Pinos Altos Range, Pinos Altos, April 12, 2018

Physcia callosa, photomicrograph of undersurface of thallus, photo Russ Kleinman & Karen Blisard, Pinos Altos Range, Pinos Altos, April 12, 2018

Physcia callosa, photomicrograph of thallus in KOH, photo Russ Kleinman & Karen Blisard, Pinos Altos Range, Pinos Altos, April 12, 2018

Physcia callosa, photomicrograph of cross section of thallus in KOH (cortex, not medulla +), photo Russ Kleinman & Karen Blisard, Pinos Altos Range, Pinos Altos, April 12, 2018

Physcia callosa, photomicrograph of soredia on downturned thallus margin, photo Russ Kleinman & Karen Blisard, Pinos Altos Range, Pinos Altos, April 12, 2018

Physcia callosa, photomicrograph of soredia, photo Russ Kleinman & Karen Blisard, Pinos Altos Range, Pinos Altos, April 12, 2018